How to use Phentermine Correctly for Weight Loss (A New Approach)

Most people are not using Phentermine, for weight loss, correctly. 

Before you jump to conclusions, let me explain:

There is a "standard" way to use Phentermine (the way that most Doctors use it) and a "better" way to use it (the way that I recommend you use it) and by simply changing how you use it, you can increase weight loss while reducing symptoms. 

If you want to know how to use Phentermine safely and correctly, while avoiding negative side effects and optimizing your weight loss, then this is the article for you.


What is Phentermine?

As a Doctor, I've always been interested in weight loss. 

To me, it seems like it's probably one of the most important conditions that patients deal with and it's insanely common. 

Losing weight helps improve quality of life, energy levels and self-confidence of almost everyone who achieves it. 

So you can imagine how excited I was to use Phentermine (a supposed weight loss medication) once I started my weight loss practice

But I was incredibly bummed out once I saw the results!

I expected patients to shed excess pounds and come back happy and healthy. 

What I found was quite the opposite: 

Some patients lost a minor amount of weight (a few pounds here and there) but many suffered from side effects which made them stop taking the medication. 

percent of patients who lose weight using phentermine by body weight

Worse yet, some patients experienced no weight loss at all. 

So, what gives?

At first, this caused me to stop using Phentermine, but then I realized that there may be a better way to use it. 

What if we can take advantage of the weight loss associated with this medication while minimizing the negative side effects all while maintaining weight loss after patients stop using it?

Sound too good to be true? 

I will explain how to do this, but first, you need to know some basics

So what exactly is Phentermine? 

Phentermine (also known as Adipex, Fastin, Lomaira, and Pro-Fast) is one of MANY weight loss medications FDA approved to treat obesity in the United States. 

It works by stimulating your sympathetic nervous system and is classified as a "stimulant" (1).

Stimulants work to reduce your appetite and increase the number of calories that you burn at baseline (your metabolism). 

Phentermine is FDA approved for weight loss if used SHORT-term and if COMBINED with diet and exercise (2).

Used in this way many studies show that it is effective. 

But we have a problem:

Phentermine works fairly well (in up to 80% of patients in some studies) but it's NOT a long-term solution. 

Phentermine is supposed to work because it suppresses your appetite

If you eat less food then you should lose weight, right?

Not so fast. 

You may lose weight, but do you really care if you lose weight if it all comes back once you stop the medication?

That's one of the biggest problems with using Phentermine. 

It may act to temporarily suppress your appetite, but whatever results you achieve while using this medication practically disappear once you stop it. 

What this means is that Phentermine is NOT a long-term solution for weight loss. 

Or is it?

There are actually ways to increase the length of time you can use it while avoiding weight gain after you stop it (more on that later). 

Does it Actually Help with Weight Loss?

From a technical standpoint, it is clear that Phentermine does indeed work to reduce weight. 

When you look at the clinical studies showing that Phentermine helps patients it's easy to get excited (3).

weight loss with phentermine use over a 16 week period

But when you look at real patient reviews you see something quite different:

Most people do admit that Phentermine can help them lose weight (in the short-term) but almost everyone puts back on the weight that they lose once they stop the medication. 

This phenomenon is well known to researchers and it is the reason that Phentermine is only approved for SHORT-term weight loss

But what good is weight loss if it's not sustained?

If you take the time and energy to lose weight it's only natural that you want that weight to STAY off. 

Even though it doesn't show sustained weight loss in clinical studies, we can still use the fact that it "works" to our advantage. 

We know that FDA approved doses do indeed suppress the appetite and do indeed alter the sympathetic nervous system (thereby increasing how many calories you burn). 

The question then becomes how can we use Phentermine correctly to lose weight in the long-term while avoiding negative side effects? 

The answer to this question has to do with how this medication is used (including dosage and frequency).

Most People use Phentermine Incorrectly

I said previously that most people use Phentermine incorrectly so we need to expand upon that idea. 

The "standard" way to use this medication is something like this:

Take 1 pill each and every morning for 30-day intervals (the maximum amount of time you can prescribe the medication). 

Each day you take it you will notice that your appetite is reduced so you consume less food. 

Because of this reduction in caloric intake, you will lose some weight (maybe a few pounds a month). 

Eventually, your Doctor will stop prescribing the medication and you will slowly regain whatever weight you lost over this 1-3 month period

Most Doctors will NOT prescribe Phentermine longer than a 3 month time period because it is well known that the benefits of Phentermine start to decline after that time period. 

So even if you lost some weight while using it initially, you will have diminishing returns on your weight loss over time. 

That means if you lost 5 pounds the first month you'll probably lose 2-3 pounds the next month and then another 1 pound the following month. 

Taking it for another 3-6 months will NOT increase the amount you lose. 

This is the "standard" way to use Phentermine and it's how most Doctors recommend that you use it. 

But there are some tweaks that I've learned over the years to dramatically improve how effective it can be. 

How to use Phentermine Correctly (The most effective method)

So how should you actually use Phentermine for long lasting and sustained weight loss?

In order to discuss how this is done you need to understand the importance of your metabolism (also known as metabolic rate) on your weight. 

Perhaps the single most important measure of whether or not you will maintain your weight after you lose weight has to do with how well your metabolism is functioning (4).

Your metabolism is a term used to describe the number of calories that you burn doing everyday activities such as breathing, sleeping, thinking, etc. 

This amount of calories accounts for up to 90% of the total amount of calories that you burn each and every day (depending on which study you look at). 

But we have a big problem. 

It's well known that CALORIC restriction is known to cause a REDUCTION in your metabolism and basal metabolic rate. 

Let's rephrase that statement to make sure it's clear:

If you consume fewer calories than whatever your metabolism is set at, your body will adapt by LOWERING your metabolism to match your food intake. 

This is known as metabolic damage and it occurs with calorie-restricted diets and is one of the reasons that up to 99% of diets FAIL (proven through studies) (5).

You might be seeing the problem here.

Phentermine causes a reduction in your appetite which WILL lead to a reduction in the number of calories that you consume. 

This caloric restriction will ultimately lead to a reduction in your metabolism AND the regaining of weight after you stop the medication. 

So how do you PREVENT this from happening?

It turns out that you can bypass this negative impact on metabolic function by altering how you reduce your calories. 

As far as your metabolism is concerned, there is a HUGE difference between SUSTAINED caloric restriction and EPISODIC caloric restriction. 

Sustained calorie restriction = 1,000 - 1,200 calorie diet daily x30 days

Episodic calorie restriction = 1-3 days per week of 500-1,000 calories

Sustained calorie restriction is the "standard" advice that most weight loss experts give and the way that most diets function. 

You temporarily reduce the number of calories that you consume for some time interval (usually 30-90 days). 

You lose some weight during this time period but you always gain it back because you damage your metabolism in the process. 

Episodic calorie restriction, on the other hand, does NOT result in damage to your metabolism (6).

Episodic calorie restriction also has the benefit of causing the same amount of weight loss associated with sustained calorie restriction. 

It's really a no-brainer in terms of which one to choose. 

But where does Phentermine fit in?

Phentermine can be used to help BOOST the effectiveness of the episodes of temporary caloric restriction by INCREASING your metabolism and by REDUCING your appetite

This combination makes using Phentermine MUCH more effective and much safer. 

You end up using a smaller dose, using that dose less frequently while still reaping the weight loss benefits. 

Even this small change can have a huge impact on your total weight, how well you tolerate the medication and more. 

thyroid metabolism reset poster for side bar

The absolute best way to use Phentermine is to combine phentermine with intermittent or prolonged fasting routines. 

Using Phentermine no more than 3 days every 7 days (at the absolute most!). 

Many patients will be fine using it only 2x every 7 days. 

The days that you use Phentermine are the days that you practice either prolonged or intermittent fasting

You can take Phentermine on the morning of and on an empty stomach to help reduce your appetite for that day. 

You can learn more about how exactly I use phentermine in my weight loss program here

It's a simple change, but one that has a huge impact on your weight. 

Before you run out and get your Doctor to give you Phentermine make sure that you read the limitations of this medication and using this method. 

Is Phentermine Safe? Side Effects to Watch out for

As much as I like Phentermine we need to be fair about the potential side effects associated with this medication. 

Because Phentermine is considered a "stimulant" it carries with it some side effects that should not be glossed over (7).

The term stimulant is used to describe the effects of medications on the sympathetic nervous system. 

The sympathetic nervous system is your fight or flight response system and it manages your energy level, blood pressure, heart rate, alertness and so on

Medications which trigger this system often result in increased focus and attention (Adderall), suppressed appetite (Phentermine), increased blood pressure, increased heart rate and increased demand on your heart in general (8).

With this concept in mind, we can talk about the POTENTIAL side effects of Phentermine, including: 

  • Heart palpitations
  • Hypertension or increased blood pressure
  • Insomnia
  • Dry mouth
  • Appetite suppression
  • Anxiety
  • Constipation or Diarrhea (depends on the person)
  • Headaches
  • Dizziness

Most of these side effects have to do with how sensitive you are to the dosing, meaning they are dose sensitive. 

In most cases, simply reducing the amount that you take is usually enough to reduce the symptoms. 

But a small minority of people, usually around 5-10%, will not be able to tolerate Phentermine at any dose. 

There are other options for these people to help with appetite suppression which you can read about here

But, as you can see, Phentermine is not necessarily a "safe" medication and it should only be used if necessary. 

You have to think about whether the potential negative side effects are worth the loss in your weight and determine if that weight loss is worth the small risk. 

In most cases, it is worth it, but if you have existing high blood pressure, heart problems or insomnia then using Phentermine may not be the best option for you.

When in doubt touch base with your Doctor. 

Limitations of Phentermine & Who Should use it

Will using Phentermine in the way I've described here result in pounds and pounds of weight loss for everyone?

Not necessarily, which is why we need to be realistic about your expectations. 

If you are someone that is NAIVE to calorie-restricted diets or NAIVE to using Phentermine then you are someone who will most likely have a lot of success with this method

By naive I mean someone who has NOT used these methods before. 

If, on the other hand, you are someone who has done the HCG diet multiple times or someone who has used Phentermine for months and months on end, then this method will likely not work well for you. 

So why does it work for some people but not others?

It has to do with the amount of metabolic damage that certain people have already sustained from bad eating and dieting habits (9).

It takes years to reverse metabolic damage and metabolic damage is often associated with other hormone imbalance such as thyroid dysfunction and leptin resistance which will need to be treated. 

If you fall into that category you can read more about how to fix it here

But for those people who do not fall into this category Phentermine will probably work very well for you. 

To recap: 

You are most likely to benefit from Phentermine if you...

  • Have never used Phentermine before
  • Do NOT have a history of yo-yo dieting
  • Are younger (less than 50)
  • Are ALSO eating healthy
  • Are ALSO sleeping well at night
  • Are ALSO avoiding/reducing stress
  • Are ALSO exercising (but not over-exercising)
  • Do NOT have thyroid disease, leptin resistance or insulin resistance

If you don't fit into the categories listed above it doesn't mean that Phentermine won't work for you, but it does mean that it probably won't be as effective as other therapies. 

What Kind of Results should I Expect if I use it?

It really depends on how you use Phentermine. 

As a stand-alone weight loss medication is just an "average" weight loss medication. 

Don't get me wrong, it can still help with weight loss, but it's probably only going to help you lose 5-15 pounds long-term. 

This is assuming that you use it as I've outlined above (with episodic intermittent and prolonged fasting). 

But it's most likely NOT going to get you to your "normal" weight, especially if you have 30+ pounds to lose

Instead of using Phentermine as a stand-alone medication I tend to use it as an additional therapy to more powerful weight loss therapies. 

I've written about them before, but you can find more information on powerful weight loss medications here

Phentermine is best used as part of a multi-faceted weight loss program which includes dietary changes, exercise routines, the right supplements and other medications. 

Phentermine can also be combined with hormonal therapy such as testosterone or T3 therapy to help boost weight loss over a short-term period. 

Dosing Phentermine (Including Pricing)

Dosing Phentermine is actually fairly straightforward. 

The "standard" dose of Phentermine is 37.5mg

This is the highest dose you should take in any given day (do NOT exceed 1 tablet daily). 

Higher doses will increase your blood pressure, heart rate and may cause heart palpitations and so on. 

Even at this dose of 37.5mg, some patients will find that they are "sensitive" to the dose and simply cannot tolerate it. 

They may experience heart palpitations, anxiety or even sleeping issues. 

For those people who fit this category just remember that the tablets are scored down the middle. 

This means you can cut the dose in half, down to 18.75mg, by breaking the tablet in half. 

phentermine tablet image

This USUALLY works for most people. 

What about the cost?

I'm all for using low-cost medications, provided they work and provided they are NOT dangerous. 

In terms of cost, Phentermine is reasonably priced (even though it is not the "safest" medication out there)

The cash price for Phentermine, provided you use a coupon service like goodrx, should only run you about $10 for 30 tablets: 

phentermine cash price

If you use Phentermine the way I've outlined above then that cost drops considerably. 


Because you're only using 2-3 tablets per WEEK. 

The pharmacies won't like it, but your wallet certainly should. 

Bottom Line

I've spent a lot of time practicing different ways to help people lose weight and this is just one of many strategies that I've created over the years. 

By simply altering how you look at your weight and what actually causes weight loss you can make changes which will dramatically impact your weight long-term. 

Standard recommendations for using Phentermine seem to be inadequate and may cause long-term metabolic damage. 

Instead of using Phentermine as recommended, consider using it in an episodic way. 

This will allow for more sustained weight loss, fewer side effects all while avoiding metabolic damage. 

I've used this strategy many times in my career and it has worked well for many different patients

Now I want to hear from you:

Are you using Phentermine for weight loss?

Is it working for you? Why or why not? 

Have you damaged your metabolism in the process?

Leave your comments below! 

References (Click to Expand)

This post was most recently updated on March 8th, 2019

Dr. Westin Childs

Dr. Westin Childs is a Doctor of Osteopathic Medicine. He provides well-researched actionable information about hormone-related disorders and formulates supplements to treat these disorders.He is trained in Internal Medicine, Functional Medicine, and Integrative Medicine. His focus is on managing thyroid disorders, weight loss resistance, and other sex hormone imbalances.You can read more about his own personal journey here.

125 thoughts on “How to use Phentermine Correctly for Weight Loss (A New Approach)”

  1. If one has insulin resistance as a result of PCOS can phentermine still be effective if combin d with an insulin sensitizer like Avandia or Actos?

    • Hi Lisa,

      The answer is maybe. When in doubt make sure you touch base with your current Doctor to help determine if it’s right for you. Each situation is different and, even though Phentermine is effective, I only use it in about 10-20% of patients. Usually, because there are other better therapies available or because it’s simply not necessary.

    • Hey Lisa, I too have Ir due to PCOS. I have been taking Metformin and restricting carb intake. This worked great for me the first time I did it, but I was younger and worked in an office. Now I’m a bit older and have a job that keeps me on my feet for 10 hours a day, so I find that a low-carb diet leaves me feeling famished constantly. I’m looking at adding phentermine to the mix, but wanted to see if you have had any results so far?

  2. Dr. Childs,

    I’ve been on Qsymia for a year, the last several months taking it only 2-3 times a week (with Dr. knowledge). I’ve had modest success with weight loss, but have hit a plateau (one reason why I’ve started taking less) but after reading your articles, I likely have metabolic damage from a variety of restrictive diets I’ve been on over the years. Hindsight …gah!

    Are there plans to cover this drug in your weight loss drug series? It’s a mix of Phentermine and Topiramate and I’m curious as to whether I’m taking it in the most effective way.

      • Dr. Childs thank you for sharing this knowledge. I am about to start a round of phentermine. I want to take using your method of 2 to 3 days a week. One thing that wasn’t clear from your article. Once taking it this way, how long should we stay on it? I currently have a 30 day supply. So should I do the 3 pills a week for 10 weeks and once that is gone then don’t take anymore? I understood you to say it’s meant for short term usage.

  3. I have used phentermine/chromium compounded formula a few times a week. I have had great success! It was a lot of work (diet and exercise) and took a bit to get my thyroid medication just right but just adding the phentermine mix to my routine I have lost nearly 40 pounds and feel fantastic! Everyone… work with your doctor to find what works for you. I am a believer!

    • Hi Michelle,

      Thanks for sharing your story and glad it worked well for you! Keep us updated on your weight loss maintenance.

      • I take my phentermine as soon as I wake up in the morning, usually, around 6 am. By 6:30 am I am rocking and rolling. By the time I go to bed around 10 PM, I’m so ready to lay down. Be consistent with when and how you take the medicine. It will help. I’ve lost 50lb in 9 months.

        • Hi Melanie,

          The concern that most people have is not that they don’t lose weight while taking it but instead that they gain it all back once they stop. The vast majority (about 98%+) will gain their weight back once they stop taking it and it’s not a medication that can or should be taken indefinitely. The purpose of this article is to help people understand how to take it so that their weight stays off after they stop taking it.

          It’s good that you’ve lost so much weight and hopefully, it stays off once you stop taking your medication.

  4. I’ve read that people with high insulin, especially PCOS women, should take a few weeks and settle into a healthy diet (higher in healthy fats, medium protein and low carbs) before trying fasting (with or without the help of phentermine). The goal of waiting a few weeks is to avoid muscle loss that can happen from starvation while your insulin levels are high. Trying to level insulin for a few weeks before fasting will hopefully burn fat instead of muscle during fasting. Is this true? If so, im a bit disappointed to not jump into fasting right away. Thanks!

    • Hi Lisa,

      I’ve never had anyone wait and it’s never been an issue so I would tend to disagree with that statement.

  5. Wouldn’t regular exercise also help to keep your metabolism from falling? There are many ways to naturally increase your metabolism. Not just changing the way you take your weight loss pill, right?

    • Hi Anna,

      Regular exercise would be helpful, but over exercising may be detrimental. Finding that optimal level can be tough and varies from person to person. Altering how you take weight loss medications don’t necessarily increase your metabolism, they just prevent you from damaging it in the first place.

  6. I have been taking phen /topamax with vitamin b12 injections 2x a week for six weeks…. The first two weeks I lost 15 lbs. easily. The weight has tapered down as expected.

    I started (5’10 220 lbs).

    I did start walking. I struggled at first walking was hard… I am now up to walking three miles five days a week and increasing the pace. I am down to 188 lbs.

    This is incredible life changing for me… I have completely stop craving sugar and bread. I was a food addict on top of this I have celiac disease. Unfortunately, i could not never give up flour and suger. Now with this medicine I feel fantastic. Not only with the weight loss but not craving sugar/wheat.

    I am aware the my weight coming off so fast coincides with no carbs. But I had no idea how sick I was from eating flour with my celiac condition.

    • Hi Angela,

      That’s awesome! Thanks for sharing your story and congrats on the weight loss. You are right that some of that weight loss is probably related to the reduction in carbs but also probably from the reduction in inflammation from eliminating wheat.

    • Hi, were you taking phentermine every day or just 2x a week as well? I’m kind of struggling to lose weight and I am the same height and was the same starting weight as you. 5’10 and 220. I am now 200 but kind of stuck and I’ve been taking phentermine for about a month now… am I using it wrong?

      • Hi Lauren,

        Phentermine is more of a short-term solution, not a long-term solution and it doesn’t work well for people who have more than 50 pounds to lose. They may lose 10-15 up front, but more changes are necessary for weight loss beyond the initial 10 pounds or so. I find it is better as a tool which can be combined with other therapies rather than a standalone weight loss therapy.

  7. Hi there. My body has been abused from over used of diet supplements since 2009. I am now 43 years old and have used them on and off to maintain my weight.

    Now recently, my weight gain has begun to increase and I have out non 6 kilos in two months.

    My eyes are puffy, face is puffy, fingers well and I am gaining weight all over. I do follow a five time a week exercise and eating right.

    My sleeping patterns are long. I sleep a lot and get fatigue every time and most of all fatigue begins in the evenings.
    Eye lids feel hevy and foggy as well,

    How do I reverse the damage I have done?

  8. [email protected]
    I’m 32 yrs 5’5 and 170. I took Phen for about 3 months and have been off it about a month now, I’ve already gained 4 lbs back this month alone. I have about 11 pills left and have already cut them in half. Do you think that with continued exercise and intermittent fasting as you suggested I could lose the weight and being in to maintain? My personal goal weight is to easily maintain 160. Thanks.

    • Hi Whitney,

      Probably not, you will most likely gain all of the weight back that you lost if you lose it based solely on calorie restriction from suppressing your appetite.

  9. Hello,

    I notice that I stop losing weight on phentermine 37.5 I’ve been taking it for about a month and lose 10 pounds but I did start with the low dose first for 2 weeks 15 mg “yellow pills”. So exactly I still have a week or so left with phentermine 37.5.

    But I stop it today after I weighed myself and gained 1 pound, just this week my doctor suggested I restrict my calories to 1200, I’m 234.pds 5’5 this isn’t working for me, I’m still hungry. So I notice all this on my own so I started to research and found your website. Please give me some advice. Oh and I’m doing low cardio exercises. It’s amazing what you said, the Dr. Will only give you a 3 month supply, and this is what my Dr. give me, I have one more prescription left.


    • Hi Faith,

      If you restrict your calories you risk causing metabolic damage which means you will gain all of the weight you lost back once you stop the medication.

  10. Can I take this with the t3 thyroid conversion booster and adrenal complex? I only take my levothyroxine but want to make sure I do this right so I do not gain my weight back when I am done.

  11. Hello, I have Hashimoto and weight loss is extremely hard for me. I have been on Phentermine for two weeks. I like to follow the intermittent method you discussed here. Here is my plan: take half of Phentermine for the next 4-5 days with about 1300-1500 calories. Then go on to the method you mention with 500-1000 calories (closer to 1000, if I exercise that day). Please let me know if you think this will be effective. I am 45, 5”5’, 180lbs. Thank you so much for putting this information out there!

  12. Hello Dr. Childs
    I am a mother of 4, 32 years and struggling with weight as long as I can remember. I am not obese but the overweight I have depresses me greatly. Over the years I have tried so many diets, checked my thyroid – which works fine, sleep enough, exercise I would not lose weight. The worst part is that I have put on 10kg in the previous 3 months. I admit that I ate whatever came my way. Lately, I heard of the medication Topomax and so I took it for 2 weeks the way my doctor prescribed it. It didn’t do anything except being angry and on a short fuse. Naturally, I stopped. After some research, I heard that Phentermine would help and so I started that by taking 1 pill a day. I exercise and watch my food closely. It is been 9 days now and I have gained another kilo. I am at witts end. I cannot describe to you how sad I am that while this medication helps so many people to me it just did the opposite. What other blood tests should I do? Should I stop with the medication, no sense to feed my body with it if it does not help? I read lots about Phentermine and came across one blogger who said that by him it just worked after a week and a half. Grateful for any advice. Eve

    • Hi Eva,

      If you have a history of dieting in the past then you may need to look into hormones such as cortisol, leptin, thyroid hormones, estradiol, and testosterone. You may find your answer in testing for those hormones.

  13. I have PCOS I feel like I’ve tried everything and nothing is working. I eat healthily, do moderate exercise every day and have a fairly active life. I’ve been on phen and lost about 13 pounds and now I’ve hit a huge stall. I think I do have metabolic problems from years of dieting. Last time I did intermittent fasting and carb cycling before being diagnosed with PCOS I gained 10 pounds. I’m afraid of doing it again for further messing up my metabolism. I am also on metformin to help stop the insulin resistance. I’m only 33 and I really want to get this under control but I feel like nothing works since I’ve had kids. Please help

    • Hi Erin,

      Make sure you look at hormones like leptin in addition to insulin. You’ll also want to look at your sex hormones as well. These hormones may be playing a role in your inability to lose further weight.

  14. Ok. So I’m trying to make sure I understand this approach. I was just prescribed Phen 37.5. I was also told to cut in 1/2 and take before 10am as not to interfere with sleep in the p.m * so you alternate your days like Mon Wed Fri would be higher calorie days (1200 caps) and Tues Thurs Saturday would be low cal/ fasting days?

    • Hi Melissa,

      That may work, but you should make sure that your calories are sufficient for your metabolism on the days that you eat.

  15. I used Phentermine 15 mg. for 60 days and lost fifteen pounds (170-155). Weighing and measuring all food, I ate about 800 calories a day. When I lose eight more pounds, I plan to eat the same foods but up the daily intake to 1200 calories a day which is likely sufficient to maintain the weight loss. I weigh myself every day and plan to restrict calories if I gain five pounds. Hopefully, I will be able to exercise more if my physical condition allows.

    • Hi Ann,

      I would be very cautious about restricting your calories that much. You may find that you lose weight now but there is a high chance (about 99%) that you will regain all that weight and damage your metabolism in the process.

  16. If you’ve taken phentermine before, how long should you wait before giving it another try for it to be effective? I can’t remember if it’s 6 months or one year.

  17. Great article! Thanks for the great info. How many calories do you recommend eating on the non-fasting/non-Phen days? I am 35 female 5’5 200lbs and need to lose 35-40 pounds

    • Hi LC,

      It’s not about the calories as much as it is about matching the number of calories that you consume to your metabolism (the amount that you burn). This value is different for each person because it depends on how badly your damage is metabolized, your muscle mass, your activity and so on.

  18. I am at least 40 pounds overweight. I was prescribed Phentermine 15mg. I do have high blood pressure but controlled w meds. I also take Synthroid for low thyroid. The first week I lost about 4 pounds. I’m on week 2 and nothing! I’m so disappointed. I stick to a 1000 calories or less a day which might be the problem. I’m going to try your suggested way of taking it and pray it helps. Side effects come and go but the benefits of me loosing far outweighed the side effects. Any suggestions are appreciated. My doc gave very little direction.

    • Hi Gina,

      If you aren’t able to lose weight despite reducing your calories down to 1,000 per day then you probably have other issues which you need to take care of. I would definitely consider looking into other hormones such as insulin, leptin, and thyroid hormone.

  19. Hello, I have been on Phentermine for almost 2 months. The first month I was on 15 mg dose and I lost 9 lbs .. month two we upped the dosage to 30mg I have lost 4 in the first couple weeks and now the last couple weeks … nothing. I eat well.. some days I’m around 1200 cal and sometimes more. I also work out 4 days a week and lift for strong women competitions. I have never had issues dropping weight till this past year and I have had blood work done and my thyroid checked and everything comes back normal. I was excited to try Phentermine but now it’s discouraging me. I’m 28 years old. I’m 5’7 and at my heaviest, I was 207 I am now down to 195. I know my body has more to lose but I’m not quite sure where to go from here. I have one month more of the medicine if I choose to take it. Any advice?

    • Hi Allison,

      If you use phentermine daily then you will almost always gain all of the weight back you lost once you stop using it. I recommend you follow the advice in this article to achieve lasting weight loss.

  20. Hello,
    I just started Phentermine Thursday night(I cut the pill in half).
    I took it to see how it would affect my sleep and my appetite.
    I was up until about 3 am the next morning and had to make myself lay down.
    I was tired but not sleepy.
    I ate but wasn’t really hungry.
    I took the other half Friday morning at 7 am(which I realize now was in the same 24 time period) and another 15 mg dose in the morning on Saturday morning.
    I did not take this morning(Sunday) because when I woke up I felt drowsy and quite high.
    I had this increased tired but not sleepy feeling yesterday as well.
    Even as I write this I have a feeling behind my eyes and every time I close them I feel like I should be asleep.
    I do get hungry but I do not have cravings or overeat.
    I have 3 kids to get off so I am quite active in the am but I did notice that after taking the pill in the morning that I am thinking about whether I should eat, I am not really hungry but this subsides within 2 hours and 32 oz of water.
    I know that these are documented side effects but with such a low dose are the symptoms due to still being sensitive and my body trying to get adjust to the medication?
    Or is it possible that I personally am just sensitive to such a low dose?
    If I hit a plateau or the meds stop working what would you recommend then?
    I am planning 15 mg MWF and 1500 a day because this is what Myfitness Pal calculated for me to lose a pound a week.
    Should I continue on to take 15 mg MWF? OR should I take 30 mg twice a week like on M and THUR?
    Alycia W.

  21. So you’re saying to fast for the three days you’re taking Phen? Do you mean no calories at all? Or up to 1,000? And what of the other days of the week? Just eat normally?

    I’ve been on Phen for two days and have eaten about 1200 calories a day. The first day I didn’t feel hungry all day. But today I started feeling hungry. I am already worried that it’s not going to work for me.

  22. Hi, I have Adult ADD and years ago I tried phentermine and it had adverse side effects as in mood swings,bad drowsiness and made me feel horrible. Having ADD my brain is wired a little different but at 43 and a food lover I have to get some weight off! Any suggestions? Thank you

  23. Hi, I have taken Phentermine about 10 years ago with success and started taking it again about 2 months ago. I have lost 10 lbs so far using only half a pill most days. When I went to my follow up appointment, I was told if I only take half of the pill, that I will build a resistance to it and it will no longer work properly. Is this true? I see you mention to use half too if a whole pill is too much for someone.

    • Hi Jennifer,

      If that were true wouldn’t you build resistance twice as fast if you took the entire pill each day? Sometimes I don’t think doctors even know what they are saying half of the time 🙂

  24. Hello Dr.,

    Just to make sure I understand the method you describe for using Phentermine 3 days every 7 days. Could I take Phentermine weekly just Friday, Saturday, Sunday?.
    How long would you recommend taking Phentermine in this way? Would it work for long term and would I need to take a break? If so, how often? I am interested mainly in maintanance since I only have about 13 lbs to loose.

    Thank you so much for your time!

  25. I was prescribed 15 mg of Phentermine. They are in a capsule form. . I lost 12 lbs the first month although it truly didn’t feel I like it. Could it have been mostly water weight? Almost finished with my second month and only down 4 lbs. I try to eat a consistent diet. Some days I feel like the pill helps a lot curb my appetite so I can make better choices when eating. Some
    Days I feel so hungry. Like nonstop hungry. Why could this be? I have tried taking it 1 hr before breakfast and 2 hours after . I haven’t noticed one way working better the. The other. I’m a very busy mom of 3 that volunteers everywhere and literally barely have time to breath. So I have bad eating habits because I’m always nonstop and rushing. I have done so much better most of the time while using oven. I don’t have the crazy psycho urge of give me anything or else. I am able to grab fruit or veggies to snack on…Thank you for your time.

  26. Thank you for the information! I have taken Phentermine before and hate the side effects so I am going to give this a try. One question, what do the other five days look like diet wise if I do intermittent fasting for two?

  27. So I am currently taking it, and in the first 2 months on the full dose I lost almost 10 pounds. But then they put me on the half dose and I have done nothing but slowly gain the weight back in the last 2 months. About 4 pounds. My resting heart rate has been abnormally high in the last month so I’m just stopping it altogether. Even on the max dose, i was still hungry. I worked more on making better choices instead of less calories and drinking more water. The increased energy and focus were great, but I dont really even get that anymore. The way you described makes a lot of sense. Wish I had known about it when I started. I’m just hoping that after stopping the drug that all the weight doesnt just come right back.

    • Hi Melissa,

      If it is used daily (as you described) you will always gain the weight back once you stop the medication, unfortunately (for reasons described in the article).

  28. Hi Westin,

    I am currently on phentermine after having my baby. I gained over 50 lbs but I have lost about 27 so far by myself before the medicine. I have only lost 4 lbs and I have been on phentermine for a month now. I take it everyday and me and husband already do intermittent fasting, that’s how I lost the 27 lbs. I’m going to try and take it only 2-3 times a week like you recommended but is there any other advice? I can’t tell that it is working anymore. I don’t exercise like I should, but I have cut out all the bad things from my diet so I don’t know how I am not doing better. Right now I am just stuck at a certain weight. Btw I am 22 years old and I am 208.5 lbs if that helps any!

    Thank you!

    • Hi Julee,

      If you’re already doing intermittent fasting and not losing weight then changing how you take the phentermine probably won’t help much. You will instead need to look into other issues such as your hormones and then treat those for the rest of your weight loss.

  29. Hi Dr. Childs,

    My question is for someone that is over 50 like myself who has a very slow metabolism, what hope do I have of losing weight. I’ve started Phentermine today and would like to lose some weight , enough to give me energy to begin this lifelong process of getting my health back. Is there any hope of getting back in shape for a pre menopausal 52 yr old? Would staggering the Phentermine be helpful or am I just sunk? I work for a physician and I’m constantly moving so obviously when I get home I’m exhausted so getting enough exercise is tough for me. Please advise and thank you for any help, guidance you can give.

  30. Do you prescribe this? I do not have a doctor where I live that does weight loss except those that sell you their meds for $150 a month.

  31. Hello!

    I have been on Phentermine for 3 months now and I have lost a Total of 36 pounds. I am 5’2” and I was 188 pounds. I went to the Doctor’s office for a check-up, and he asked if I had anything I wanted to talk about and I mentioned my weight. I had gained 15 pounds in just a few months. I didn’t ask for any solution, it was more of a comment of “wow, I gained a lot of weight very quickly” and then my doctor suggested the Phentermine. I was scared to death to take it as I am not much of a pill taker. I don’t like how most pills make me feel. Well, the first day I started the Phentermine I also decided that I was going to change the way I eat and exercise. I have had zero side effects from the pills, with the exception of the first few days where I was a little shaky, but not bad at all. Now the weight loss has drastically slowed down., (I’ve lost 3 lbs in the last few weeks) my doctor gave me one last month of Phentermine. My question is, should I wean off of it? Or just stop taking it once the 30 days is up?

    • Hi Deanna,

      I typically don’t recommend that it’s used in the way you used it because once you stop you will likely gain your weight back, but to answer your question, it’s usually better to slowly wean off of it.

  32. I‘m so happy to have read this advice. I am on my second day (5”4’ 158pounds) and have lost 4 pounds already on 1200 cal a day. I’ve haven’t yet taken today’s pill (I’m cutting in half the 37.5 dose and only taking 1/2 a pill) but can still feel it in my system from yesterday, so was wondering if I should just skip today’s dose and try and go it alone. I’ve also been thinking how to stretch out my prescription because I know I’ll have a hard time getting it prescribed at a lower weight, but then I feel that’s when I’ll need it most, to not gain the weight back!

    • Hi Onday,

      I would be very careful in reducing your calories on a daily basis. If you do you will most likely gain all of the weight back once you normalize your diet and you may only lose 5-10 pounds at most.

  33. Hi Dr Westin,
    I just came across your article in my search for answers as I’m a long thyroid sufferer and thave been on Duromine 30mg on and off for the last 3years.
    I’m 56, and 5’4″ had my thyroid and 16 lymph nodes removed 4years ago due to papilliary thyroid cancer which had spread, I also hit menopause within 6months of the surgery and radio-iodine treatments .
    I’ve been on the Australian brand of synthyroid replacement hormone Eutroxsig 100mg daily since then.
    I didn’t feel well for a number of years leading up to the surgery and even worbse afterwards, when I rapidly gained an extra 10kgreached 94kg with in 12months after the surgery.
    Not able to drop any weight due to my very damaged metabolism I finally convinced my doctor to put me on Duromine. I managed to lose the 10kg over the first 3months with Duromine then started to gain once off it. So I would go back to doctor for another 3months dose and this has been going on for two years.
    The Duromine is no longer effective in losing weight but it helps me maintain my weight and it has been very effective as pain relief for my severe joint pain….and that’s why I keep taking it cause when I stop for a week I can barely walk as my knee pain comes back. I also have brittle nails, thinning hair, joint pain, swelling/ fluid retention in my knees and the list goes on….
    I still need to lose weight and and feel better and I was hoping for some guidance from you regarding intermittent fasting with Duromine and which of your supplements might help me.
    Also, do you supply to Australia?
    I look forward to your reply

  34. Hi there! I was reading the article and I had great results. First, I started going to the gym and watching what I ate. I weighed 300lbs I lost 10lbs on my own. My doctor prescribed phentermine and over a 3 month period, I increased my exercise to 6 days a week. I lost 60lbs while on the medication. Overall I’ve lost 88lbs total since I started in July 2018. I joined Weight Watchers online in December and have lost from that as well. My biggest question would be can he prescribe the meds again? I still have 60 more lbs to go. I’m still considered obese. I want to get rid of the visceral fat. I responded so well to the drug that I know I would do great again.


    • Hi Amy,

      Yes, he/she can prescribe it again. I worry that you will probably regain all of that weight once you stop weight watchers, however. So be careful if you decide to use it again as it may make your situation worse.

  35. Can you also take blood pressure medicine with this. I’m not on blood pressure medicine but it does slightly raises it. I do take Turmeric to lower pressure which helps.

  36. Can you please give me an example of how much fasting should be done on the days I take Phentermine…. would it be best to fast completely on these days or just Fast the last part of the day .. please explain.

  37. I’ve been taking Phentermine for about 13 days now, two weeks. And I’ve only lost 9 pounds so far… is that normal? Or? Because I feel like I can be doing more right now.

  38. Mr. Childs,

    I have been on phentermine for approx 6 months with a daily dose of 30mg. I have limited by calorie intake to around 1500 a day and try to work out cardio and weights 2-3 times a week, and practice IF 5 days out of 7. I started at 396lbs and am now at 271lbs. Have had zero side effects.
    Question: is the use of phentermine for 6 months standard? Somewhat concerned with the other research I have done to be on the drug for that long of a period?

  39. I’ve been using Phentermine for 9 months. I was always very fit and healthy until 10 years ago when I had my thyroid removed because of cancer. I gained 25 lbs. and never felt “good”. I’ve lost 20 lbs. and am planning to lose 5 lbs. to get to my ideal weight of 140lbs.5ft.6.and currently 145lbs.

    I was very depressed and despite exercise and healthy diet, I couldn’t lose weight. This has been life changing for me. I’ve been exercising but not as hard as I could. When I reach 140 lbs., I plan to increase the frequency and intensity of my exercise as I stop taking the Phentermine.

  40. My doctor put me on phentermine 37.5 mg and the first 2 weeks I lost 13 lbs. But then I had a bad cough and mixed it with cough medicine and thought I was having a heart attack. So I got off it for 2 weeks and gained 7lbs back. Now I’m on it again and I’m really not losing any weight and I’m barely eating anything. Am I doing something wrong? In the morning I have a bowl of cereal then around 2 pm something small and then dinner something small to eat. So I will try and do the meds every other day and see how that works. My doctor also gave me topiramate to take at night any suggestions? Thank you.

  41. Hello,

    This is a great article. I used phentermine with success losing 50 pounds back in 2011. Successfully kept it off until a work injury and massive amounts of steroids in 2015. Now I’m back on to re-lose the weight. I cycle my doses. 1 full tab, 1- 1/2 tab then a day off during active weight loss. After meeting my loss goals I kept a script on hand for “reset” days. After large gatherings or any times I would for some reason overeat, phentermine helped me fast for a day to reset my appetite. I believe phentermine can be used in this way to maintain long term loss and indeed it worked for me for 4 years. Again though during those 4 years I only needed it maybe once a month.

    • Hi Mrs. Wit,

      It can definitely help some people, but remember most people are not as fortunate as you are when they take it. I would say the majority of people do not have the success you did, but there will always be some (probably 5-10% of people who use it) who will be able to lose weight and keep it off while using it.

  42. Should I try phentermine a second time? I’ve never been much of a dieter despite battling obesity due to PCOS. But two years ago my mother started having medical issues related to her weight, and I could see that in my future as well. When I stepped on a scale just before my 44th birthday and saw 325 lbs, I decided that it sucked that I could no longer go hiking, something I used to love, or even walk the two blocks to the post office so I bought some good shoes and started walking. I cut out the Red Bull I was drinking at work because I work a graveyard shift. I lost 30 lbs in three months. Started to stall out, joined a fitness club and added in strength training 2-3x/week. Lost another 20 lbs. Stalled out. Went to a bariatric clinic that primarily pushes surgical solutions, but didn’t/don’t want surgery. After the first few months of losing a couple of lbs, and a lot of testing, including resting metabolic rate testing, I did a three-month course of phentermine. I took it only on the nights I worked (4 nights/week) It helped me stop all snacking, and in fact, I had to force myself to eat. No adverse effects. It didn’t dramatically increase my weight loss, but I steadily continued to lose weight (25 lbs on phentermine, even lost 8 lbs the first month after I stopped taking it. But now, at 80+ lbs down over 13 months, I’m stalled out again. I fell back into my eating for comfort habits after a family crisis. I’m considering asking my doctor to give me phentermine again so I have a little help getting back into seeing food as fuel instead of emotional support. It’s not about the calories, but about why I am eating more than I need to.

  43. Hello Dr.
    I would like to share my experience with you. I was on Phentermine for 6 months. At my start Weight I was 412.7 lb. Could barely function at that point. 6 months later with a very strict diet and a complete lifestyle change I am down a hundred and seventy pounds. After a month of no Phentermine I don’t have any food cravings. I haven’t gained my weight back and actually I’ve lost 7 lbs since I’ve stopped taking Phentermine. I just wanted to share this perspective with you. Because you see a lot of negative things online about this pill and granted it can be some nasty stuff. But I’m one person that is extremely grateful for the benefits of this pill. Not to mention a complete lifestyle change with the pill.

    • Hi Matt,

      Thanks for sharing! I don’t know if the information on this particular post came off as negative towards the pill because if that’s the case it wasn’t my intention. Phentermine CAN be a great asset for some people, but it can also be seriously detrimental in others. I am happy that you’ve had results, but I would be careful because if you are going to gain weight it will be in probably another 6-9 months (the weight gain doesn’t occur immediately after you stop taking your medication). I hope you are one of the lucky few that keeps your weight off, but if you are like 99% of other people, you may regain all of your lost weight in another 6-9 months or so. If you’ve changed your lifestyle dramatically then you should be able to keep the weight off, however.

  44. Hi! I am 5’11 and weight 289 pounds. I also have high blood pressure controlled with medication. I have been on phentermine 30 mg for 4 weeks now and am down to 273. I also added exercise back into the routine this week with walking and light aerobics. I don’t want to be on this medication too long and know the risks especially with a high blood pressure history. What is a good time to be on this medication?

  45. Hi, I found your article to be very informative, thank you for writing it. I weigh 160 want to get to 130 by May. The weight loss clinic said totally achievable. I have never done a diet or pills. The first month I lost three pounds every week! The clinic was like yay great! But I had an instinct that this was wrong. I felt good, but that nagging instinct told me to re asses.

    I take this pill every other day now, I’m very concerned about gaining back the weight afterwards. I plan on reading more of your work to figure out my situation. Thank you for being so informative.

  46. Hello Dr. Childs, Thank you for this site and information. My question is about whether taking phentermine twice a day, one in the am and one at noon is more effective? I have had some nausea with taking the 30mg capsule in the am. That nausea can be ameliorated with eating something with it such as sugar fee Jello. However, my biggest issue is eating late at night. I am wondering if a two-dose regimen would work better because it would last longer and prevent late evening hunger. Also, I saw a study about a phentermine/topiramate Qsymia. What is your opinion about that combo? Thanks so much!

  47. Hi I start tomorrow I’m currently doing the fasting. I don’t eat until 12pm and I stop at 8pm so do I continue this and just take the phentermine three times a week? How many calories should I consume?

  48. I have taken phentermine off and on for a few years – I restarted it recently and about two weeks after starting it my feet and ankles have become swollen during the day – they do go down while I’m asleep at night but the next day that become severely swollen again. I have quit taking the medication – will this go away?

  49. I loved this article. I used to weigh 210 I bs. I got down to 137 pounds. I had to stop the phentermine because my doctor only allows you to be on it for 6 months then take a break and you can go back on it. This article is point on. I gained 20 pounds back in 2 months. I ate high protein low card diet while taking it and I continued the same structure of eating after. No matter what I did the weight piled on. I want to sustain my weight loss so I am going to try the one you recommend of 1000 calories a day. I haven’t eaten bread, pasta, grains or any kind of flour, etc for 14 months. If I do eat these type of items I get super sick. My body won’t tolerate them anymore. I started back my phentermine yesterday and I lost 5 pounds since yesterday morning. I ate a large piece of turkey meatloaf with sauteed veggies in it. I don’t eat any sauces either. I use ranch ( low in carbs or Italian dressing). My favorite go-to seasoning is Cavendars. If you haven’t tried it buy some. I use it in everything I cook and no carbs or super low in carbs. I need to know exactly how to keep my metabolism up after I stop this medication again. I do not want to gain the weight back. I have a very physical job but I also have MS and I wonder if MS can affect my metabolism. When off the pills I still ate healthily but I also can not eat any fruit. Is there a diet plan with menus that are available that I could follow while taking phentermine and so I can follow them after? If not please write a meal plan book. You could make some big bucks writing it. Thank You for your time.

  50. Today is my first day of taking Phentermine. I’m glad I came across this website as I begin this prescription. I gained 25 lb over the last five years and I believe it’s due to hormonal changes. I began taking small dose of estradiol. I feel I’m pretty active most the time. Never in my life have had a weight problem I’m 57 always been in the range of 110 to 115 pounds. I noticed that you had said that you no more about hormonal changes in our women’s this is kind of a sensitive subject but, my husband and I haven’t had sex in 5 yours and I have no real desire to have it as well. Last time we did have sexual intercourse it was very very painful and I do not want it now for sure. Is there anything I can do to change this I would like to have intimacy again as it’s killing our relationship as well but I don’t want to have it if it’s very painful I feel that losing weight might be help me feel more desirable may be needed or wanted for now I know my husband doesn’t want that. He tells me don’t lose weight on my account cuz it won’t change anything on how I feel about you. Sounds like I need a divorce what do you think? I guess I just wanted to hear it another person’s opinion other than family and friends
    If you know of anything that could help me to gain more intimacy I want to get a least I would be eternally grateful. I spoke with my physician about it and she the nurse practitioner and didn’t say anything on how it could help or I could be helped by it.

  51. Hello. I am from Poland I would like to order / buy phentermine. Do I have to have a prescription for a med…

  52. Hi Dr. Childs,

    I have been taking a half-dosage of phentermine for almost 2 weeks now and have lost about 10 pounds. (Currently 5’4″ and 180-punds at 50 yrs old.) I exercise 5-6 days a week and an already pretty active. The half-dose is working to stave off hunger a bit, but I still have to work at it. (Calorie counting, drinking lots of water and herbal tea help me feel full, etc..) I was just about to move to a full dosage when I came across your blog and a better way to use the drug. (The last thing I want is to damage my metabolism and/or reach the end of my prescription limit – I assume my dr. will take me off of this after a couple of months – only to gain the weight back.) My questions are:

    1- should I move to taking a whole dose 3x a week (eating 1000 calories those days)? Or stay with half-dose? I am asking from a standpoint or rev’ing up the metabolism on those days. Plus, it’s already very hard for me with a half-dose eating 1400-1600 calories a day because I do exercise (spin or strength training for an hour).

    2- Assuming a do the 3x a week phentermine (1000 cal) and 4x a week no pill but restricted diet (1500-1600 cal a day) – how long can I take phentermine? Indefinitely? In other words, is a half-dose (or a whole dose) 3x a week for a long period of time safe if I’m otherwise healthy?

    Incidentally, I have had zero side-effects. No trouble sleeping, no dryness, no head aches – nothing.

    Thank you in advance for your time answering.


  53. Wow, it’s a little overwhelming with all the comments. I used phentermine back in 1996 when it was mixed with Pondimin not sure of the correct spelling back then it was called phen-phen. I lost over 85lbs on it in 3-6 months. It worked great and I kept off the weight until I got pregnant. Then it was a major struggle and I got up to 309 my all time heaviest. I had gastric bypass in 2001 I was around 25 years old. I got down to 138 but seemed to stay more at 150 usually. Had another child in 2010 and still managed to get the weight down until the last few years. I noticed that after I had novasure (surgery) I really started to gain weight? Which I had because I am iron b12 anemic from my bypass and the monthly cycle had gotten so bad they couldn’t get my blood levels stable. Well, here I am age 43 and learning how terrible it is to get off at this age. I am currently taking phentermine 37.5 mg been on it for a month now and down from 212 to 200. I wouldn’t say I even overate, it was less active if anything? However, I am back on treadmill 6 days a week and walking my neighborhood every night and feel like I’m gonna collapse at the time lol. My doctor says the novasure wouldn’t affect the weight but I really disagree. I am eating a 1000 calories a day and walking over 13000 steps a day and it’s barely budging now? Love my Fitbit it has been a huge help, it even tells me I’m burning over 2400 calories a day. So why isn’t it coming off? In the past week, I have not lost a pound? Trying so hard to not get discouraged but it’s so depressing to be at a standstill already.

  54. Hello,

    I’m looking forward to changing the way I take Phentermine. I have a few questions:
    How long do you recommend taking the Phentermine in this way (3 months or longer, until my 3 month Rx runs out)?
    My Dr also put me on LDN.
    Will this combination help my weight loss efforts?

    Thank you!

  55. Um, thanks for not answering my questions to you. Darlene got her answer the same day!! I know you probably don’t have time to answer questions…so don’t have that feature enabled. What a disappointment.

    BTW, I’m not interested in hearing answers from you now.

    • Hi Kate,

      Sorry about that! You are correct in your assertion that there are just too many questions and not enough time on my part but I do feel that answering some questions is better than answering none.

  56. Hi, I’m currently on lisinopril 20mg for high blood pressure. My Dr.suggested Phentermine 15mg for weight loss. Is this safe for me?

  57. Hello! I was happy to stumble across your article online. Thank you for taking the time to offer your experience and expert advice on this medication! My question is, have you ever noticed any differences; with yourself or your patients, in taking the brand name of phentermine(Adipex-P) vs. the generic brand? I have used the generic brand in the past(2009) having great success, dropping 35 pounds in 8 weeks and keeping the weight off for 7 years. I started taking the generic brand medication about 2 months ago but I’m struggling to get to my goal. My doctor is now having me try the name brand(Adipex-P) to see if this may help with my results. I know you stated that using this drug more than once lowers your chances for weight loss success. But, I’m hopeful that if I try your method of intermittent fasting and lowering the amount taken weekly, I can reach my goal. One thing I have noticed with taking Adipex-P vs. the generic brand is that I seem to have less of the undesirable side effects that the generic brand gave me!

    Thank you for your time,

    • Hi Valerie,

      I’ve never noticed any difference but I also use it differently than most people. I only ever use phentermine as a way to augment other weight loss therapies instead of relying upon it solely for weight loss. I wouldn’t be surprised, though, if some people did better on one over the other.

  58. I have the same question as Pam that hasn’t yet been answered. I take Phen while fasting the same 3 consecutive days each week (Mon-Wed). Then I eat as usual without it the remaining 4 days. Is this the correct method you’ve outlined?

    By the way, I am one of the 98% you’ve described, having lost a lot of weight on Phen only to regain it all back. I’m an avid exerciser and the calorie in vs calorie out hasn’t worked for me. I tried so hard and NOTHING seemed to keep me from gaining all the weight back. I’m hopeful your method will help me with keeping weight off forever this time. But need to make sure I’m doing it right! Will you please confirm?

    • I have been on phentermine for 5 months, with this month being my 6th month. I have had great success with taking them and exercising. I have lost a total of 70 pounds. My doctor said that is the most she had had a patient lose over the course of being prescribed the medication. I did practice an intermittent fasting, lower carb, and a calories in calories out approach.
      My only concern is I have heard taking it longer than 6 months can be damaging and there hasn’t been many studies on taking it long term. As of lately, I have been experiencing symptoms of insomnia, heart palpitations, and nausea. I have cut back on taking it almost completely, with back draws. I have seen an increase in cravings and calories. My doctor didn’t seem too concerned and wants to keep me on it as long as I am losing such high numbers.
      I’m worried to cut back and begin gaining like so many others I have heard about.

      • Hi Jessica,

        If you start to gain your weight back it will be a few months after you stop taking it. It will start slow and just a consistent weight gain each month. If this occurs it’s from metabolic damage from appetite suppression.

  59. I just got home from the doctor and weight in at 407 lbs… I am the heaviest I have ever been in my life
    :(. My doctor suggested this and my first reaction was why am I just now hearing about this!! I am reading a few places that we should be supplementing phentermine with some potassium. Any idea why or what the recommendations are for the amount of potassium. I assume because you might lose a significant amount of water weight you might also unknowingly be dehydrated so it’s just for the purpose of electrolytes? A doctor I am not so I am open to being corrected on my thought process :). Just so I am clear again on this, you recommend taking it 2-3 days a week where you are also IF’ing. What would we do on the non-phentermine days just watch our intake? I have done IF to include OMAD (one meal a day) numerous times but I have a big problem with stopping eating. So even though I was fasting I’d wipe out the good work.

    Also, exercise my plan is to do lifting 3 days a week would I be smart to make lift days non-phentermine days or will it give me the kick I need.

    Thanks for your response I have the prescription filled and I’m just sitting here looking at it and doing all the research I can.

  60. Like everything you say is the same. Like we will all gain it back. Wow, thanks… You’re a good dr. way to shut anyone down. Your comments will make anyone depressed.

    • Hi Tracie,

      I’m not trying to make anyone depressed but I also feel that I need to provide accurate information. The problem here is the mentality that so many people who come to this page have when it comes to weight loss. They are fundamentally looking at it incorrectly which is leading them down the wrong path. This article is really just the beginning and I would recommend anyone reading this to check out my other articles which help explain why this mentality is the problem:

  61. Hello, I’ve been using phentermine for longer than I care to admit. One thing I know about this medication is that it works when I do, in other words, when I’m serious about weightloss, it definately helps but if I’m just taking it for energy, I can eat alot while taking it. Junk food/sugar cravings aren’t the same as hunger and I think that has something to do with it if that makes sense. I’ve also noticed that different brands or forms act differently. Gelcaps are weaker than capsules of the same strength and some forms don’t work at all if you eat before or within an hour of taking it. I feel normal on phentermine, no side effects but I feel sluggish without it. I was treated for hyperthyroidism over 20 years ago (it’s now normal, not slow) so maybe I had just been so accustomed to hyperthyroidism and that’s why phentermine just makes me feel normal-still helps with weightloss though when I’m committed.

  62. Dr. Westin,
    My name is Jimmy, 5’11” 46 yrs old used to be athletic, was 369 lbs on Jan 5th this year 2018 & now 290 lbs as of Aug 1st – lost 81 lbs so far & at least 60 lbs to go to my target! For me, this is a disciplined behavior. I do take Levothyroxine for hypothyroidism bordering T3-T4 & took that months before starting my diet plan. When starting Phent., I also started the CMWL shake & Food bar program. I drank 3 shakes & ate 1 bar for 3 days over the first weekend (that was 4 per day, each having 25%daily nutritional value including protein), combined with the Phent helped prepare me mentally & physically for discipline & routine. Then I started eating the SmartOnes or Healthier frozen or prepared dinners(lowest sodium I could find) only for lunch that had some veggies & little carbs & protein, yet still drink my shakes in the morning, afternoon, & eat food bar with a shake for dinner. I also saved a lot in food cost from what I had been spending! I take my Levo late at before bed with a glass of water at least 2-3hrs after eating anything cause I know vitamins & minerals may cause it not to work properly – taking on an empty stomach I believe is key, at least that’s what I’ve found best for me. In the mornings I take 2 ALIVE gumi multivitamins, an 81mg aspirin, & my doctor has me on Lisinopril (which I had already been on before my weight loss). My Doc. doubled my lisinopril from 20mg to 40mg to counteract the rise blood pressure effects of the Phent, which ended up working out just right for me. After losing 60lbs in 4 mths, I found myself eating more regular food & eating at night, & then I plateaued, gaining 3 lbs. After a serious discussion with my Doc, he prescribed Topiramate to work as a catalyst with Phent & now I’m back to my discipline of vitamins as soon as I get up (5am), prepare my mind, spirit, & body for the day (I’m a bi-vocational minister & insurance broker), 1cup coffee in the morning with food bar, then take most meds at 7 am; at 10am drink health shake & take Topiramate & Phent; 12noon eat small lunch of SmartOnes dinner or 6″ Subway club sandwich with lots of veggies; 3pm another shake; & 6pm a shake & food bar, OR a very light supper that has some form of green veggies, or salad with vinegarette dressing. Now, I’ve stumbled on to what you are talking about when you said to fast a few days a week using Phent on those & eat moderate (reasonably) those other days in between. Some days I’ve found myself so busy that I’ve forgot to eat because I just wasn’t hungry & when I was drinking just shakes, my mind was trained that was all I needed nutritionally anyways, so I didn’t eat any regular food. On those days, however, I went to bed feeling skinny ( if that makes sense). Those are the days I was more sensitive to my clothes being loose, my rings loose, my feet freezing cold at night in bed, & my hand being cold. My Doc & his wife who’s also a nutritionist said that was because of lack of calories, so he said put some low-fat milk in my powered mix shakes to vamp up my calories & eat more selective carbs in moderation. ANYWAYS, this past month, I’ve been more physically active, found myself eating a little more, but spread out, more energetic & active, having lowest recorded blood pressure ever on my medical records (124/83) & lost another 10lbs! At 290 I feel & agile like I’m 200, but I still can’t dunk a basketball like I used to 🙁 This is a goal of mine when I get back down to my weight goal. My Doc is now recommending me to do some light to moderated weight training, but no cardio at this time. He doesn’t want me to over-do & loose more rapidly than I already have. With increasing milk in my shakes, adding more protein & carbs to my diet, & me wanting to get toned again, he said weight training & muscle stretching exercises would be best for now until I my body got used to the routine in a few months, then as I get closer to my goal, I would get winged off the Topir & Phent & may reduce my Lisinopril as ad in cardio exercise mixed with weight training & stick to my food plan of shakes, bars, fruits & nuts, small portions of healthy foods during day, & greens at night.
    Any suggestions & recommendations are welcomed that I need to discuss with my doctor. Thanks!

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