Does Synthroid Cause Alzheimer's Disease?

Does Synthroid Cause Alzheimer’s Disease?

Research has shown that people with hypothyroidism are two times more likely to develop Alzheimer's disease when compared to those with normal thyroid function. 

In addition, some newer studies have suggested that there is a link between taking thyroid medication and developing dementia.

This link has caused some people to believe that it is actually the medication itself which is causing dementia. 

In this article, we are going to explore why I don't believe that this is the case, 

Quick Highlights from the article:

  • Hypothyroidism is a known and reversible cause of Dementia
  • Inadequate treatment of hypothyroidism (with not enough medication) may be the cause of dementia in people taking thyroid medication. 
  • Thyroid hormone and prescription medications differ in how they are processed by your body which is why you can't compare the side effects of synthetic medications to hormone medications.
  • You can prevent dementia by ensuring that your dose of thyroid hormone is adequate and by finding a doctor who understands a better approach to thyroid management.  


Inadequate Treatment or Negative Side Effect? 

We are going to discuss this topic in detail, but I want to first start out with my opinion: 

My current belief (which is subject to change) is that thyroid medication does not CAUSE or CONTRIBUTE to Alzheimer's disease. 

Instead, it is much more likely that an inadequate treatment with thyroid hormone, causing low thyroid status in the body, contributes to dementia and not long-term use of the medication itself. 

There are only a handful of studies which link the development of dementia with the use of thyroid medication. 

And these studies do not include a significant number of people (the study that we are going to be using today only included a few hundred). d

With such a low number of people in the study, it reduces the power and efficacy of the study while increasing the chance that the results were seen only by chance (and not associated with the medication itself). 

Let's dive into a little more detail and talk about what we know: 

We know that people taking thyroid medication do indeed seem to have an increased risk of developing dementia long-term. 

There's only a handful of studies which show this connection, but we still have to at least consider the fact that it is possible. 

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These studies simply show that people who take thyroid medication end up with Alzheimer's disease slightly more frequently than those people who do not take thyroid medication. 

This connection has led some researchers to believe that thyroid medication is the thing CAUSING dementia in these people. 

But is that a fair assessment?

Isn't it just as likely that those people taking thyroid medication were not adequately being treated?

After all, we know that hypothyroidism is a REVERSIBLE cause of dementia (1) and something that all doctors are trained to look for. 

hypothyroidism is a reversible cause of dementia

It is well known that hypothyroidism can mimic Alzheimer's disease and it is something that should be evaluated and treated in all patients with dementia. 

Isn't it possible that these people who are taking thyroid medication are experiencing this side effect because they are not taking enough thyroid medication? 

I strongly believe so, and even the authors do suggest that the dose of thyroid hormone that you are taking may play a role. 

They are operating under the standard conventional wisdom that thyroid status in the body can be measured adequately with the use of TSH and T4. 

They suggest that people with high T4 (suggestive of hyperthyroidism in their eyes) have an increased risk of developing Alzheimer's. 

The only problem with this suggestion is that it is possible to have low thyroid function even with a high or normal T4. 

And this problem can occur if you are someone who has problems processing thyroid medication or converting T4 into the active T3 thyroid hormone (see the section below). 

We also know that patients with Alzheimer's have low levels of T3 (2) (even within the normal range), indicating the importance of this hormone over other hormones such as Free T4. 

Due to the confusion regarding thyroid treatment and management, it's possible that many patients are being under-dosed (unintentionally) with thyroid medication which may lead to lower than normal free T3 levels which can increase their risk of developing dementia or Alzheimer's disease. 

It is also possible that some people are receiving too much medication (those with an extremely suppressed TSH) which may also cause further confusion among patients who are being overdosed. 

This is important because hyperthyroidism is another well-documented cause of early onset dementia (Alzheimer's type) (3). 

Understanding Thyroid Medication

To highlight the importance of T3 you need to have a basic understanding of how T3 functions in your body. 

T3 is the active thyroid hormone and is, therefore, the most important measure of thyroid function in your body. 

If you do not have a sufficient amount of T3 to turn on genetic expression in your cells (and in your brain) then you will suffer from the symptoms associated with hypothyroidism. 

Free T3 should be differentiated from other thyroid lab tests and measurements including TSH (which is commonly used), Free T4, and thyroid antibodies. 

Free T4, while important, is not nearly as biologically active as T3, which means that measuring the value of free T4 is only helpful if you also measure the value of free T3. 

Both free T4 and free T3 are created and produced by your thyroid gland, but most of the free T3 in your bloodstream comes from the conversion of T4 into T3

Using this pathway your body can create T3 on demand and exactly as much as it needs. 

Several processes, such as obesity, leptin resistance, inflammation, chronic illness, prescription medications (and so on), limit how well your body can turn T4 into T3. 

If you understand the importance of T4 to T3 conversion, then you can start to see how the measurement of high free T4 in patients with Alzheimer's may not point to a problem of hyperthyroidism, but a problem of proper T4 to T3 conversion. 

If your body can't convert T4 into T3, then it will build up a large store of free T4 with inadequate or low levels of T3. 

But because physicians do not routinely order free T3, this problem may be misdiagnosed or missed in a great many patients. 

Hormones vs Prescription Medications

There is also a big difference between the use of hormones and the use of prescription medications. 

While hormones do require a prescription to obtain from your pharmacy, they are not the same as prescription medications. 

Prescription medications are man-made medications which have some desired effect on the body. 

But, they differ from hormones in one very important way, they are not natively found inside of the body which means they are a foreign substance. 

Let's use lisinopril (a blood pressure medication as an example). 

Lisinopril is used to help lower blood pressure in people who have high blood pressure. 

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Lisinopril works by inhibiting a specific enzyme in your body known as ACE (angiotensin converting enzyme) which helps lower blood pressure. 

It's important to understand, though, that lisinopril is NOT naturally found within your body. 

You can compare this to hormones which ARE found natively in your body, such as thyroxine (another name for T4) or sex hormones such as estrogen/progesterone. 

When you take these hormones (medications), your body knows exactly what to do with them, it knows how to process them, and it knows how to eliminate them. 

Your body doesn't necessarily have the same pathways set for synthetic or man-made medications. 

And this is one of the reasons why prescription medications have negative side effects.

BECAUSE they are not a "normal" substance found inside your body. 

But what about thyroid hormones? Do they cause side effects as well?

The answer is yes, but for an entirely different reason. 

Hormones can cause side effects when taken, but they cause side effects if you take either too much or too little. 

The medication itself should NOT cause any serious or negative long-term side effects because your body knows how to metabolize it and utilize it. 

Medications like lisinopril, however, cause side effects for two different reasons:

#1. Because they are a foreign substance which you are ingesting

It should go without saying that ingesting a foreign substance may cause negative or unwanted side effects. 

This can range from increasing your risk of cancer to causing intestinal distress. In either event, this can stem from how your body processes and attempts to break down the medication. 

And #2. Because they can cause side effects related to the purpose for which you are taking them

Imagine taking a blood pressure lowering medication designed to "normalize" your blood pressure. 

What happens if you take too much? You might start to experience the side effects of low blood pressure such as dizziness, lightheadedness, or you might pass out. 

These negative effects are not caused directly by the medication itself but instead, they are a consequence of the effect of the medication (in this case lowering your blood pressure). 

Because thyroid medication is a hormone which your body knows how to process, it should only cause side effects which are dose-related. 

Sometimes you can experience mild side effects such as stomach upset or nausea which is related to fillers and binders in your thyroid medication, but these are infrequent. 

That means most people experience negative side effects when taking thyroid medication because they are not taking enough or because they are taking too much. 

Should you Stop Taking your Thyroid Medication? 

You may be tempted to stop taking thyroid medication after reading this, especially if you have a family history of dementia or Alzheimer's disease. 

I would strongly recommend against this course of action for several reasons:

#1. Abruptly stopping your thyroid medication can be harmful to your health! 

I've discussed the side effects which can occur when you stop taking your thyroid medication on my blog before and I would encourage you to read this post for more information. 

Basically, what happens when you stop taking your thyroid medication is that your body is unable to produce enough thyroid hormone on its own due to the suppression which your thyroid medication was causing on your pituitary/hypothalamus. 

This sudden drop in thyroid medication may cause symptoms such as weight gain, increased fatigue, hair loss, cold intolerance, and so on. 

These symptoms tend to persist (or worsen) for the first 4-6 weeks as your body attempts to make thyroid hormone on its own. 

It can take several weeks for your body to "warm up" and produce its own thyroid hormone and during this time you will most likely feel very poorly. 

#2. Stopping your thyroid medication will cause hypothyroidism which may only further increase your risk of dementia

Even if your body can produce SOME thyroid hormone, it doesn't mean that it can produce ENOUGH thyroid hormone to sustain your cells and body. 

There is a reason you are taking thyroid medication in the first place, and this reason is to help substitute the normal amount that your thyroid can generate. 

I've already mentioned previously that hypothyroidism is a potentially reversible CAUSE of dementia and when you stop taking your thyroid medication you are putting yourself into a state of hypothyroidism. 

So, even if we assume that Synthroid or levothyroxine can cause dementia, it's much more likely that you would develop dementia or Alzheimer's more rapidly if you stopped taking your medication. 

#3. It's better to test thyroid function with a complete thyroid lab panel

Before you stop taking your thyroid medication, you should get a complete thyroid lab panel which extends beyond the normal tests for TSH and free T4. 

As you look at other tests, such as free T3, total T3 and reverse T3, you can get a better idea as to how your body is processing the thyroid medication you are currently taking. 

With this information, you can make a better decision about what type of thyroid medication may be beneficial for your body

Up to 20% of the general population may have trouble with standard thyroid medications like Synthroid and levothyroxine, due to genetic variations which can limit how well they convert T4 into T3 (4). 

You can test for these genetic issues by looking for specific SNP's (single nucleotide polymorphisms) and by getting basic genetic data from companies such as 23andme

If you already have your genetic information I would recommend that you compare your results to this list of SNP's which are known to interfere with thyroid function in various ways. 

What can You do to Prevent Dementia if You are Taking Thyroid Medication? 

The best way to ensure that you live a long and healthy life is by looking at more than just your thyroid. 

While your thyroid is certainly an important contributing factor to your long-term memory health, there are also other factors which are entirely within your control!

Whether you are young and concerned about your memory or even if you are in your 60's and 70's and experiencing a reduction in your memory, these steps can help improve your memory and reduce your risk of developing dementia: 

  • Adequately treat your thyroid: I've touched on this already but your first step should be to adequately treat your thyroid. For many of you, this will mean using a combination of both T4 and T3 thyroid medication. You can start by mimicking the ratio of T4 to T3 thyroid hormone production that your thyroid produces naturally which is around 80% T4 and 20% T3 (5). These recommendations are counter to current clinical recommendations given by conventional physicians but you will most likely find that as you approach this ratio that you will see an improvement in all of your symptoms. Make sure that you also pay close attention to lab tests such as Free T3 and Total T3. As long as these values stay in the "optimal" range, thyroid hormone should be able to do its job. You can find a downloadable pdf on how to find a competent thyroid doctor here
  • Look at other risk factors (genetics): There are many other risk factors which can increase your risk of developing Alzheimer's and perhaps the most important is the APOE gene. You can test for the presence of this genetic mutation which can help you understand your risk more clearly. The presence of this genetic mutation would be much more concerning than the presence of hypothyroidism or the fact that you are taking thyroid medication. 
  • Lower and manage your insulin and blood sugar: Plenty of newer studies have linked the progression of dementia to glucose metabolism and insulin resistance (6). This isn't an ideal situation given the fact that so many people suffer from these conditions, but the silver lining is that this particular issue is modifiable through certain lifestyle changes. You can reduce your blood sugar and treat insulin resistance by changing up your diet, using certain medications, and by utilizing specific supplements. If you are overweight (even 15-20 pounds) there is a high probability that you also have insulin resistance. You can identify the presence of this condition by testing both your blood sugar and your fasting insulin. 
  • Try meditation: Meditation may be one of the single most effective strategies you can use to reduce your risk of Alzheimer's. Meditation helps reduce the impact of stress on your body by modulating serum cortisol. Recent studies have also shown that meditation can improve your sleep, reduce depressive symptoms, reduce anxiety, reduce inflammation, improve your immune system, and reduce insulin resistance (7). Pretty good for a free therapy which only takes 10-20 minutes per day! If you aren't already meditating then you are missing out. 
  • Start young: Lastly, the best thing you can do is to start YOUNG and aim for PREVENTION of dementia. Once dementia starts to show symptoms it may be too late to reverse the condition (but you may still be able to slow it down). Your best bet is to prevent it from ever occurring. If you have multiple risk factors then you should start with the therapies listed here by at least age 40-50. 


My purpose for this article is to try and persuade you that Synthroid does NOT cause Alzheimer's. 

Instead, I believe that the increased risk of developing dementia in people with thyroid disease is more likely related to how well managed their thyroid disease is. 

While it is true that those people who have hypothyroidism have a much higher risk of developing dementia over-time, it doesn't mean that it WILL happen for sure. 

My recommendation is to take the steps outlined above and do your best to mitigate all risk factors which are known to contribute to the development of dementia. 

As you mitigate these risk factors, and as you improve your own thyroid function by optimizing your medication, you should see your risk of developing dementia normalize to that of the general population. 

Now I want to hear from you:

Are you worried or concerned that you will develop Alzheimer's disease?

Do you have any other risk factors (weight gain, insulin resistance, genetic predisposition)?

What things are you going to do (or are you currently doing) to reduce your risk?

Leave your questions or comments below! 

References (Click to Expand)

do thyroid medications cause dementia?

About Dr. Westin Childs

Hey! I'm Westin Childs D.O. (former Osteopathic Physician). I don't practice medicine anymore and instead specialize in helping people like YOU who have thyroid problems, hormone imbalances, and weight loss resistance. I love to write and share what I've learned over the years. I also happen to formulate the best supplements on the market (well, at least in my opinion!) and I'm proud to say that over 70,000+ people have used them over the last 6 years. You can read more about my own personal health journey and why I am so passionate about what I do here.

P.S. Need more help? Check out my free thyroid downloads and resources.

11 thoughts on “Does Synthroid Cause Alzheimer’s Disease?”

  1. Alzheimer’s Disease runs in my family which puts me at increased risk. I am post-thyroidectomy due to papillary thyroid microcarcinoma for which I am currently in suppression therapy. Do you suggest no suppression therapy to avoid recurrence of thyroid cancer in order to decrease my risk of developing Alzheimer’s Disease? Recurrence of thyroid cancer vs Alzheimer’s Disease…what’s better?

    • Hi Donna,

      Having a suppressed TSH doesn’t necessarily mean that you are hyperthyroid as hyperthyroidism is more of a physiologic cellular state than criteria which are met by certain labs. In terms of which is more important depends entirely on you. You would want to sit down and map out the potential outcomes of both disease states and determine which is better given your wishes and long-term desires.

  2. Hi Westin, enjoyed your articles. I had my thyroid radiated, due to not being able to suppress it and having graves disease, losing weight, etc. in 2010. I lost my 20-year job due to my problems with my thyroid issues. It is better now, and I can go for about 3 to 4 months before it gets out of range, either hypo or hyper. I tend to feel better on the hyper side. I did recently have an ultrasound and found that I had no thyroid at all due to the RAI procedure in 2010. Currently, my Synthroid was at 75mcg the last 4 months, with dosing at 75mcg daily and 1/2 of that on Sunday, which is 487 mcg weekly. I recently went from 4.2 to .35 for my bloodwork. So, my dosing was changed to 478 weekly, taking 50mcgs daily adding up to 475 weekly with alternate dosing, I feel good, but is there a better way of dosing, and is this sporadic but mathematically correct way ok? I think taking 1 pill one day, then 2pills the next day, then 1 each for next 2days, then 2pills the next day, then 1 1/2 the next day seems just odd. Thank you for listening. This wasn’t at all brief, lol? I appreciate your wisdom!

    • Hi Gloria,

      I rarely ever find that dosing in that way is necessary. There are always ways around that type of dosing by using other thyroid medications. I really only see that type of dosing with certain endocrinologists who are trying to chase the perfect TSH.

      • Thank you for replying. Can you recommend/expand on what type of medication could possibly be better? Or, is there a blog that already addresses dosing? Thank you so much for your time and your answer!

  3. Hi Dr. Westin.
    I was wondering about taking Armour thyroid versus Synthroid. It sounds like you recommend natural hormones over synthetic drugs. I have no symptoms since I’ve been taking 15 mg. everyday, but I was hoping to eventually stop all together with proper diet. Is this possible or should I continue to take Armour thyroid? Appreciate your response. Thank you.

    • Hi Julie,

      I really don’t think the distinction between “natural” and “synthetic” is actually very helpful at all. For instance, how can you say something is “natural” because it comes from a pig thyroid? Is that really natural? At the most basic physiologic level both synthetic medication and natural thyroid medication look identical, so does the source really matter? I honestly don’t think so. It’s more about dose and what works best for the patient which is why I use both types.

      • I have been researching Levothyroxine induced Dementia. Because my 86 year old mom was diagnosed with Dementia years ago after being put on the drug for low thyroid function. I take care of her when I’m not working. My daughter took care of her for two days and forgot to give her her medicine. She was so lucid those two days. We all noticed a remarkable difference. She didnt want to sleep all the time, wasn’t confused, knew who we were, wasn’t filled with anxiety. She woke up at 8 am like she used to and went to bed at 10pm with a one hour nap. She didn’t ask me 100 questions all day long. Knew what things were called. She new her name, age, answered our questions right away with clarity instead of saying “I dont know”. She sat and watched a 2 hour movie with us and laughed at all the jokes and said how funny the movie was. Normally she won’t pay attention to what we are watching on TV. She has no concept of time usually but those two days she did. She said “Its not time for me to go to bed yet, and I’m not tired”. I dont think it was a fluke. It was a wonderful 2 days. It was such an improvement that I dont want to give it to her anymore. But I did give it to her and she went right back to being confused and asking us who we were and wanting to sleep all the time. It broke my heart to see her go back to being confused all the time. I think in her case that drug brought on her dementia and id like to have my mom back. At least 75%. I talked to my client who is a pharmacist and he said something dont seem right. If she was that lucid for that long I should talk to her doctor and get her off that drug. I want to talk to her doctor and get her off of it and onto a completely different one to see if her memory is better. Id like to see her memory improve like it did those 2 days. I would bet my bottom dollar it would! More study’s need to be done with Levothyroxine and Dementia.

        • Hi Mary,

          There are many people, especially those that are older, that can get off of their thyroid medication. It would be worth looking into in your case!

  4. My 82 year old mother has recently begun showing signs of dementia. She also began taking levothyroxine in the past year. Do you think there could be a connection. What should I ask her doctor?

    • Hi Stephanie,

      It depends on the type of dementia and her symptoms. Low thyroid function can cause brain fog which may mimic dementia in an older person but you’d need more information to be sure.


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