Levothyroxine Overdose: Signs You Are Taking Too Much

Levothyroxine Overdose: Signs You Are Taking Too Much

Levothyroxine Only Works at the Right Dose

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Levothyroxine is the #1 most prescribed thyroid medication on the market. 

As you probably are already well aware, levothyroxine is prescribed to treat cases of LOW thyroid otherwise known as hypothyroidism. 

Levothyroxine works by providing your body with the thyroid hormone that it isn’t able to create on its own. 

Sounds good, right?

Well, it can be, provided you are using the exact right amount. 

I like to refer to thyroid hormone as a “Goldilocks” hormone. 

In order for you to feel good, you need to take the exact right amount. 

Take too much and you may start to feel hyperthyroid

Take too little and your symptoms won’t disappear and you will remain fatigued. 

But when you find the exact right amount, your symptoms should subside and everything should feel right again. 

Unfortunately, getting to the right dose is easier said than done and can take both time and a little bit of knowledge. 

Today we are going to focus on what happens when your dose is too high and the type of symptoms you will start to experience if this happens. 

You will learn:

  • What your symptoms tell you about your dose of levothyroxine
  • Warning signs that your thyroid medication dose is too high
  • What to do if you experience any of these symptoms
  • And how excess thyroid hormone negatively impacts your body

Let’s jump in…


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Signs of Levothyroxine Overdose

The first thing I want you to know is that being overdosed on levothyroxine is not nearly as common as not taking enough thyroid hormone. 

Because doctors know that taking too much thyroid hormone can be dangerous, they would much rather err on the side of giving you too little

So MOST people taking levothyroxine end up with persistent symptoms of hypothyroidism despite taking the “right” medication for their body. 

Having said that, there are certainly some people who DO take too much levothyroxine and this article is for those people. 

Whether you are taking too much levothyroxine or if you are just really sensitive to thyroid hormone, these are the symptoms you may start to experience as your dose of thyroid medication creeps higher and higher. 

#1. Irritability

One of the first symptoms people experience when their thyroid is off is a general sense of irritability. 

Irritability can be felt on if your medication is too high or too low but it tends to be more associated with higher doses and hyperthyroidism. 

Unfortunately, irritability is a non-specific symptom and can also be associated with plenty of other conditions and issues so just experiencing irritability by itself doesn’t guarantee that you have a problem with your thyroid dose!

It is an extra piece of information, though, so it can be helpful, especially if you are experiencing some of the other symptoms below. 

#2. Hair Loss

Hair loss is another big symptom that can be associated with both high and low thyroid medication. 

The good news is that the type of hair loss that occurs with both conditions is different. 

When your dose of levothyroxine is too high your hair will become dry, brittle, and start to crack. 

You may also notice that the quality of your hair starts to change. 

The quality, the texture, and even how it lays on your head can all be impacted by your thyroid medication dose. 

This is different from when your dose of levothyroxine is too low. 

When your dose is too low you will notice that your hair just sort of falls out by the handful. 

You will notice that your hair falls out when you shower, when you comb your hair, and so on. 

Even though both conditions result in hair loss, the type of hair loss is actually different. 

This is really helpful because the type of hair loss that you are experiencing can help you figure out the CAUSE. 

To complicate things further, you should also be aware that levothyroxine itself can cause hair loss

This hair loss is variable and can mimic the type of hair loss when your dose of thyroid medication is too low or too high. 

I have articles that outline how to reverse hair loss in thyroid disease that you should take a look at if it’s one of your primary issues. 

#3. Anxiety

Another common symptom that people with excess thyroid hormone in their body experience is anxiety. 

It may sound counterintuitive but thyroid hormone can amp up the body. 

Thyroid hormone is really a source of pure energy but too much of that energy can result in nervous energy or a jittery sensation. 

This jittery sensation is often enough to result in anxiety and even panic attacks in some individuals. 

The higher your dose of levothyroxine the more amped up you will feel and the more prone to anxiety you will become. 

The exact opposite is true when your levothyroxine dose is not high enough. 

If your dose is too low then you will tend to feel depressed or suffer from depression

As your level of thyroid hormone decreases you may start to experience slow thoughts which is sometimes referred to as brain fog

#4. Insomnia

As your dose of levothyroxine increases, it will become more and more difficult for you to fall asleep and have a restful night’s sleep. 

When you are really amped up and you have the sort of nervous energy that I talked about previously, it will be hard for you to calm your body down to fall asleep at night. 

If you are having trouble calming down your mind at night, if you are having racing thoughts, and if you find that your heart rate is elevated when you try to go to sleep, then that’s a good sign you should take a look at your thyroid medication dose. 

Insomnia can also be tricky because it is another one of those non-specific symptoms. 

There are plenty of other conditions, including other hormone imbalances such as menopause, which can make it difficult for you to get enough sleep. 

So don’t just look at how well you are sleeping as a gauge of your dose. 

You need to put it together with the other symptoms we are discussing here today. 

#5. Muscle Weakness

Muscle weakness is hard to miss but it’s also associated with insufficient dosing of your levothyroxine. 

This is another non specific symptom but it is one that you should be aware of. 

#6. Fertility issues

Infertility is another big one (1) and this problem is associated with both taking too much levothyroxine and not taking enough levothyroxine. 

How can you tell them apart?

The easiest way is to look at the length of your menstrual cycle. 

Women who are taking too much levothyroxine tend to have more RAPID cycles (2) compared to whatever is normal for them. 

For example:

Imagine that you are running on a 28-day cycle. 

If your dose of levothyroxine was too high then your cycle would become more rapid your cycle would fall to 20 days. 

Unfortunately, this rapid cycle does NOT allow for normal ovulation. It doesn’t allow for the normal peaks of various hormones such as progesterone and estrogen and it is these problems that lead to infertility

It’s simply not possible to become pregnant if you are NOT ovulating. 

The exact opposite is true when your dose of levothyroxine is too low. 

In this case, your cycle would become prolonged and would not happen as frequently. 

Using the 28-day cycle as a guide, if your dose is too low then your cycle would occur every 40 days. 

But, again, this scenario also causes issues because it doesn’t allow for ovulation. 

How can you tell if your thyroid medication dose is interfering with your menstrual cycle?

All you need to do is keep track of it!

If you started levothyroxine and your menstrual cycle has been around 27-28 days for the last 2 years and suddenly it is now occurring every 20 days then you know you have an issue. 

#7. Rapid Heartrate

This symptom is probably one of the most common symptoms associated with high doses of levothyroxine and is most likely the first symptom that you are likely to notice. 

As your thyroid hormone medication dose increases, your heart rate will start to increase as well. 

You may or may not notice this change, however! 

One of the best and easiest ways to measure how well your thyroid medication is working is by checking your resting heart rate on a daily basis. 

When I put thyroid patients on T3 thyroid medication I always have them keep track of their resting heart rate


Because it helps me to know how well that medication is getting into their body and how well it is working. 

Over time, I better see that heart rate increasing as a patient takes more and more thyroid medication. 

If the heart rate doesn’t increase then I know that there is some sort of issue either with absorption or thyroid conversion

Keeping track of your heart rate can also help you determine if your dose is TOO high. 

A normal resting heart rate in the 70’s indicates that your thyroid is probably doing just fine. 

A resting heart rate in the 50’s usually indicates your thyroid medication is too low (assuming you are not extremely fit). 

And a resting heart rate higher than 85 is usually an indication that your thyroid medication/levothyroxine dose is too high

The best time to check your heart rate is FIRST thing in the morning right after you wake up. 

This information does not apply if you jump out of bed and start doing jumping jacks and then check your heart rate. 

You should be aware that often times an elevated heart rate can go completely unnoticed which is why keeping track of your heart rate is so important. 

Nowadays, you can use tracking devices such as an Apple Watch or Fitbit, or various other wearable technology to keep track of this information for you. 

If you have any sort of thyroid problem make sure you are keeping track of your heart rate! 

#8. Heart palpitations

While an elevation in your resting heart rate may go unnoticed, it’s highly unlikely that you will miss heart palpitations!

The good news is that even though they may freak you out, heart palpitations are typically harmless. 

Heart palpitations simply mean that you are feeling the sensation of your heart beating in your chest. 

Yes, it may feel like your heart is beating OUT of your chest but they are almost always harmless. 

No, just because you are feeling your heart beating in your chest doesn’t mean that you are having a heart attack or that anything is wrong with your heart. 

It is just the sensation that your heart is beating. 

It can get confusing because if you aren’t used to feeling your heart beating you may believe that your heart rate is elevated but this isn’t usually the case. 

Whenever anyone tells me that they are having heart palpitations, I always ask them to check their resting heart rate. 

In MOST cases, their resting heart rate is completely normal which means that they are simply feeling their heart beating. 

Why does levothyroxine result in heart palpitations? 

Remember, thyroid hormone amps up the body and it does the same thing to the heart. 

There are special cardiac receptors that are sensitive to thyroid hormone. 

When thyroid hormone latches onto these receptors it can actually increase the force of contraction of the heart (3).

It’s not that the heart is beating too fast it’s just that each beat is stronger than before. 

This tends to fade fairly rapidly, though, as blood levels of thyroid hormone fall. 

But what I want you to know here is that MOST cases of heart palpitations are harmless even though they may feel scary. 

#9. Diarrhea

Next up is diarrhea or loose stools in general. 

Thyroid hormone, and, therefore, levothyroxine, help to control the kinetics of your bowels. 

The kinetics of your bowel simply refers to how quickly your intestinal tract is moving. 

The more thyroid hormone you take the faster your bowels will move and the less time your “food” will stay in there. 

More thyroid hormone and levothyroxine = looser stool

Less thyroid hormone (or hypothyroidism) = more solid stool

In this way, hypothyroidism tends to lead to constipation and hyperthyroidism tends to lead to diarrhea. 

But, of course, this all exists on a spectrum and it is proportional to your dose. 

What do I mean?

If your dose of levothyroxine is only mildly elevated then you may only experience slightly loose stools. 

If, on the other hand, you are taking way too much levothyroxine, then you might experience full-blown diarrhea. 

#10. Heat Intolerance

Another important side effect is that of heat intolerance. 

As your levothyroxine dose increases and becomes too high you will notice that you are simply not able to tolerate the heat. 

If you are taking levothyroxine and you feel like you are flushing, or sweating, or feeling like you are having hot flashes, then it may be that your dose is too high. 

These symptoms are all associated with heat intolerance. 

Another good way to tell if you are having issues with heat intolerance is to do the “heater test”. 

If you find that you simply cannot stand having heat blown in your face then you need to evaluate your dose!

Most people taking levothyroxine struggle with cold intolerance and are often too cold all of the time

Cold intolerance is a sign that your dose of levothyroxine is not high enough. 

What to Do If you Have These Symptoms? 

So what should you do if you find that you have many of these symptoms?

The good news is that the treatment is actually incredibly easy. 

All you have to do is lower your dose!

As you lower your dose your symptoms of levothyroxine overdose will subside fairly rapidly. 

You should be aware, though, that each dose of levothyroxine will stay in your system for about 4 weeks total (4). 

You won’t experience symptoms of overdose for that long, however, but it may take you some time to find the correct dose because of this. 

Whenever I would treat patients who were taking too much thyroid medication (of any type), I would simply have them avoid taking their medication for a few days to allow the thyroid hormone levels to fall. 

Once you stop taking your medication for a few days you can then re-start back up on a lower dose than what you were taking previously. 

From there you can re-check your thyroid lab tests including your TSH, free t3, free t4, and reverse T3, to see where you are at. 

Don’t be surprised if a dose of thyroid medication that was previously working for you is now too much for your body!

This happens from time to time and you shouldn’t expect your dose of levothyroxine to stay static throughout your life. 

Is your Dose Too High or Too Low?

As I mentioned previously, it’s far more common that thyroid patients are not taking enough levothyroxine as opposed to too much but it definitely does happen. 

The good news is that it is fairly easy to tell if your dose is too high and the solution is also quite simple. 

Reducing your dose should fix your symptoms within a few days. 

And now I want to hear from you: 

Do you think your dose of levothyroxine is too high or too low?

Are you experiencing any of the symptoms listed above? If so, which ones?

Are you taking levothyroxine or Synthroid? Do you find that you are more sensitive to one over the other?

Or are you using an entirely different type of thyroid medication and still having some of these issues?

Leave your questions or comments below! 

#1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3136077/

#2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5980701/

#3. https://pubmed.ncbi.nlm.nih.gov/9064969/

#4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6193522/

warning signs your levothyroxine dose is too high

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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 80,000+ people have used them over the last 7 years. You can read more about my own personal health journey and why I am so passionate about what I do.

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