I can’t think of a more scary headline for a thyroid patient than to hear that the very thyroid medication they are taking may be associated with a heart attack.
This is especially important when you consider that heart attacks tend to impact older generations and that up to 25% of people over the age of 60 have a thyroid problem (1).
But is there really a connection between using thyroid medication and your risk of a heart attack?
Sort of, but it’s much more complicated than you might think.
There’s no question that there is a complex and intimate relationship between thyroid function and heart function and when there is an imbalance in your thyroid it will impact your heart.
But that doesn’t guarantee that you will get a heart attack and it certainly doesn’t guarantee that the medication you are taking will increase your risk.
Let’s talk more about the connection between your thyroid and your heart, how it impacts your risk of heart attack, which thyroid medications are considered to be safe, and much more.
Will Taking Thyroid Medication Give You A Heart Attack?
First off, let’s answer the question about whether or not taking thyroid medication can trigger or cause a heart attack.
The answer is yes, but only if you are grossly misusing your thyroid medication and only if you have underlying problems already present.
Here’s what I mean:
Thyroid hormone directly impacts the heart tissue which means that it has the potential to increase both heart rate and the force of contraction of your heart.
In other words, taking thyroid medication can increase how quickly your heart is beating and how strong each beat is.
But beyond this, there is a very important and complex relationship between thyroid function and your overall heart health (2).
To give you a better idea of what I’m talking about here are just a few ways that your thyroid helps to regulate heart tissue:
- By impacting the flow law which directly impacts multiple cardiac parameters (blood pressure and heart rate).
- By impacting the structure of the heart and its conduction system (remember your heart is a massive electrical conduction system).
- By impacting the autonomic nervous system (both the parasympathetic and sympathetic nervous systems).
- By impacting the renin-angiotensin-aldosterone (RAAS) system.
- By impacting vascular compliance.
- By impacting vasoreactivity.
- And by impacting renal (kidney) function.
You don’t need to understand what exactly each of these functions means but you should understand that your thyroid is required if you want to have a healthy heart.
You should also understand that if your thyroid is dysregulated either because your thyroid is too high or too low that will have a negative impact on your heart.
I think it’s best to think about it like this:
A healthy thyroid means a healthy heart.
Yes, other problems can arise with your heart from outside of your thyroid but as long as your thyroid is optimized then you know those problems aren’t coming from your thyroid.
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Understanding Heart Attacks & What Causes Them
With that in mind, I want you to think about the average person and their risk of a heart attack.
Heart attacks, referred to as myocardial infarctions, occur when you have a blockage of arteries that supply blood to the heart tissue itself.
There are many different causes of heart disease but the #1 cause of heart attacks in developed countries stems from a build-up of cholesterol in the arteries (3) that supply blood to your heart.
This is referred to as coronary artery disease and is really the thing you should be worried about if you are worried about your risk of a heart attack.
Cholesterol buildup in the arteries of your heart takes a long time to develop and it isn’t until they reach complete occlusion (or blockage) that you finally get your heart attack.
The rate at which your arteries build up this cholesterol is dependent on your genetics, general lifestyle, the foods you are eating, how much stress you are under, and underlying hormone imbalances (men and women develop heart attacks as their sex hormones decline).
Are you following me so far?
If you’ll notice what I said, I mentioned that it’s the build-up and the blockage of these arteries from cholesterol that causes the heart attack.
So let’s put this into perspective:
When your doctor says that thyroid medication may give you a heart attack they aren’t saying that the thyroid hormone is the cause of that heart attack, they are saying that it may precipitate the heart attack.
But let’s be clear:
Taking thyroid medication is not going to cause the build-up of cholesterol which is the underlying cause of most heart attacks!
In fact, there’s good evidence to suggest that the use of thyroid medication may balance your cholesterol and protect your heart.
For this reason, it doesn’t make sense to blame a heart attack on thyroid medication because it’s just the thing uncovering the underlying problem which is the cholesterol build-up.
Make sense?
Thyroid Medication and Its Impact On The Heart
Let’s talk more about how thyroid medication influences your heart, though, because this topic is important.
All thyroid medications have the potential to put a strain on your heart (4), especially if they are used incorrectly.
And it is this unneeded and unnecessary stress which may unmask the presence of cholesterol buildup much in the same way that a cardiac stress test can.
But the way that thyroid medication impacts your heart is no different from the way that doctors intentionally stress out your heart with a cardiac stress test.
Doctors will frequently place patients who they think have a risk of heart disease on a treadmill (5) to intentionally put stress on the heart.
During a stress test, doctors can see if blockages are developing in the heart tissue and how well oxygen is making it to your heart cells.
And, believe it or not, there are patients who do end up having heart attacks during their stress test.
But you wouldn’t blame the stress test for the heart attack, it was just the thing that uncovered the problem that already existed.
Does this mean that thyroid hormone is dangerous because it has the potential to put stress on the heart?
Not at all!
Your body needs that thyroid hormone (otherwise you wouldn’t have been given it!) and excess stress from thyroid medication can be avoided when the medication is dosed appropriately.
It’s absolutely the case that excessively high doses of thyroid hormone may put unnecessary stress on your heart but, as long as you are being dosed appropriately, this is not a risk you have to worry about.
We know this because healthy people have thyroid hormone flowing through their veins all of the time and their thyroid is not the thing that causes their heart attack.
And when your doctor gives you thyroid medication, he or she is trying to bring you to a normal state, not give you more than you need or less than you need (though they can make mistakes from time to time).
The bottom line?
If you are taking a normal physiologic dose of thyroid hormone then you don’t have anything to worry about.
Thyroid medication, if used correctly, will not increase your risk of heart disease.
In fact, it is far more likely to protect your overall heart health.
It does have the potential to unmask underlying heart disease but really only if your dose is too high.
The Relationship Between Hypothyroidism, High Cholesterol, and Heart Attacks
If you are someone taking thyroid medication then you are doing so to treat a condition called hypothyroidism or low thyroid function.
And if that’s the case, there’s a lot of evidence to suggest that not treating your thyroid is far more likely to increase your risk of a heart attack than using thyroid medication.
Here’s what I mean:
Low thyroid states result in high cholesterol.
In other words, the lower your thyroid function is the higher your cholesterol will be (6).
Thyroid hormone is responsible for helping your body to break down and metabolize cholesterol.
When you don’t have enough thyroid hormone in your body, there will be a build-up of cholesterol which can then make its way to the places you don’t want it (such as your coronary arteries).
So, as you might suspect, treating low thyroid function should reduce your risk of heart attack and that’s exactly what we see in some studies.
Some studies suggest that early use of levothyroxine in conditions like subclinical hypothyroidism (7) may reduce the risk of a heart attack for some patients.
This suggests that even small changes in thyroid function are worth treating and their treatment prevents heart-related complications.
To be fair, there are some conflicting data as to whether or not it’s a good idea to treat subclinical hypothyroidism (8) to prevent heart disease, but the greater point still stands:
Treating patients with true hypothyroidism does provide a benefit to overall heart health.
The Difference Between T4, T3, and T2 On the Heart
What about different thyroid medications? How do they impact your heart?
This is a really important topic so let’s spend some time understanding it.
All of the major effects of thyroid hormones on the heart are mediated by T3 thyroid hormone (9).
This is very important because the majority of you reading this aren’t even taking medication that contains T3.
Most thyroid patients take T4-only thyroid medications like levothyroxine or Synthroid.
This means you aren’t even taking the type of thyroid hormone that has the potential to impact your heart directly!
In order for your levothyroxine to have any impact on your heart, your body must first convert it into T3 thyroid hormone through the thyroid conversion process.
This means that an extra step is required before your medication can impact your heart.
As far as thyroid medications go, T4-only thyroid medications like levothyroxine and Synthroid tend to have very little direct impact on the heart.
This is not true of medications that contain T3 thyroid hormone.
If you are taking a thyroid medication that contains T3 such as Armour thyroid, NP Thyroid, Cytomel, or liothyronine, just to name a few, then those medications can have a direct impact on the heart without the need for thyroid conversion.
This is why these types of medications tend to result in heart palpitations much more frequently than medications that only contain T4.
In addition, these medications also tend to have a more pronounced effect on heart rate which is why I recommend keeping track of your heart rate while using them.
This does not mean these medications are dangerous, though, it just means that they should be used with care.
Some doctors will tell thyroid patients that T3 medications should be avoided because they cause heart attacks but this isn’t true either.
Yes, they do have a slightly higher risk of unmasking existing heart problems compared to thyroid medications like levothyroxine but as long as you are not taking an excessively high dose or pushing yourself into a hyperthyroid state then the risk is essentially non-existent.
Remember:
The body naturally produces both T4 and T3 thyroid hormones so replacing both of these hormones if you don’t have enough is quite safe.
Similar to T3 thyroid hormone, T2 thyroid hormone does appear to have an impact on the heart tissue.
This effect is only seen with very high doses of T2 (10) (around 800 mcg per day) which is far higher than any thyroid patient would typically get.
For reference, my T2 thyroid support supplement contains 100 mcg of T2 in each capsule which means you’d have to take 8 capsules each day for months on end before you’d even put yourself at risk.
This would be true of any thyroid hormone, though, as you can imagine that taking 8 times your dose of levothyroxine or liothyronine would have similar effects on your health.
Heart Palpitations Don’t Automatically Mean Your Dose is Too High
Many thyroid patients, perhaps even you reading this right now, have experienced heart palpitations after taking thyroid medication.
While they may feel scary and unpleasant, heart palpitations are almost always harmless (11).
A heart palpitation is just the sensation that your heart is beating in your chest.
Because thyroid medication can increase both the rate of contraction and the force of contraction of the heart, it’s not uncommon for thyroid patients to experience heart palpitations on occasion, especially after taking thyroid medications that contain T3.
But what you need to know is that having a heart palpitation is not the same as having chest pain or experiencing a heart attack and most heart palpitations are 100% harmless.
That doesn’t mean they are always harmless, though, which is why you should always get them checked out if you are experiencing them.
If your heart palpitation is related to your thyroid medication it will tend to fade within a few hours as your body uses and metabolizes the thyroid hormone that you just took.
Should You Worry? Not If Your Dose is Optimized
In summary, while thyroid medication does have the ability to impact your heart, this effect is almost always beneficial and not harmful.
There are rare situations in which pushing your body into a hyperthyroid state or taking too much thyroid medication may negatively impact your heart health, but this can be avoided by ensuring that your dose is adequate.
In rare situations, it’s also possible for the use of thyroid medication to unmask underlying heart disease but this is also very rare and is not something that thyroid patients really need to worry about.
Now I want to hear from you:
Are you concerned about the connection between thyroid medication and your heart health?
Do you have a personal history of heart disease?
Do you feel that your thyroid is playing a role in your cholesterol metabolism or cholesterol level?
Are you planning on making any changes to your thyroid routine after reading this?
Leave your questions or comments below!
Scientific References
#1. nature.com/articles/s41598-019-49540-z
#2. ncbi.nlm.nih.gov/pmc/articles/PMC6851449/
#3. ncbi.nlm.nih.gov/books/NBK537076/
#4. accessdata.fda.gov/drugsatfda_docs/label/2012/021924s006lbl.pdf
#5. cdc.gov/heartdisease/coronary_ad.htm
#6. pubmed.ncbi.nlm.nih.gov/35038435/
#7. jamanetwork.com/journals/jama/fullarticle/2768464/
#8. ncbi.nlm.nih.gov/pmc/articles/PMC7609906/
#9. ncbi.nlm.nih.gov/pmc/articles/PMC4318631/
#10. ncbi.nlm.nih.gov/pmc/articles/PMC4272398/
#11. pennmedicine.org/updates/blogs/heart-and-vascular-blog/2019/december/heart-palpitations
Interesting. I’m taking a 1 grain does of NP Thyroid and doing pretty well on it. My key symptom, beyond slow weight gain, was very low heart rate (related to the electrical aspects of my heart, with all the impacts/symptoms that come with it). I also have mitral valve prolapse syndrome and an MTHFR variation (have experienced symptoms of adrenal fatigue for years). After my first dose, 1/2 grain, the doctor raised my dose. About eight weeks in, after my heart rate had been all over the place from the start of NP, it settled down to a range within 5 bpm, but I do experience palpitations though they seem to be moderating. The variation in rate appears related to activity level (I’m a very active 62 year old and hate to have to slow down). It’s good to hear this can improve over time. When patients are experiencing palpitations and still haven’t seen the weight start to come back down, what do you usually recommend? BTW, I do use B.I. estrogen/progesterone cream, though I think the estrogen is a bit high (have cortisol on the higher side, so progesterone is probably a little low right now).
Hi Ruth,
It depends on the situation, really. You’d want to check for other factors to see if more than just your thyroid is contributing to your weight. It’s rarely ever the case that it’s just a thyroid problem.
Sounds like she has estrogen dominance and cortisol problmes which both can contribute to wt gain or difficulty losing weight.
People talk about high cholesterol causing heart attack, but it isn’t as simple as that, and with people having thyroid issues I think that should be clarified. As I understand it what is more indicative of the likelihood of a heart attack is the ratio between HDL and Triglycerides. I have high cholesterol 288 and hypothyroid but I am not concerned because my HDL is high and triglycerides low. I also check out on a fairly regular basis my Homocysteine levels as well as C-reactive proteins both of which can be indicators for inflammation and ultimately heart issues as well as others like Parkinson’s and Alzheimer. Have I understood this incorrectly?
Hi Angela,
The most sensitive marker for predicting cardiovascular disease is your apo B level, not your HDL:triglyceride ratio. A high HDL can be protective, but it isn’t automatically so. More important than your HDL number is the function of your HDL particles but standard lipid testing doesn’t give you that information. A high HDL can be associated with increased absorption of choelsterol in the gut which predicts an increased risk of heart disease.
You’d need to get your apo B level tested and then look at other markers such as campesterol and sitostreol to see if you are a hyperabsorber of cholesterol.
You can learn more here if you’d like: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11019329/
And here: https://www.restartmed.com/should-you-take-a-statin-if-you-have-hypothyroidism/
How do I know if I need to lower my thyroid medication? What is the best protocol of tests in your opinion? Thanks Dr!!!
Hi F,
Please see this article for more information on that topic: https://www.restartmed.com/levothyroxine-overdose/
I’ve been having heart palpitations when I wake up in the middle of the night. I’ll get up go to the bathroom get back in bed and my heart is racing 110 bpm and I feel slightly winded. Once I lay back down my pulse will come down this can last for hours. It’s been going on for months. My TSH is 1.140; Free T3 2.5, Free T 4 1.73, total T3 72, Thytoglobulin <1.0. On nights that this doesn’t happen in the middle of the night, in the morning my pulse is on the high side and tends to level off as the day goes on. Endocrinologist doesn’t want to make any changes until I’m checked out by a cardiologist. My blood test don’t give a indication of heart disease. I’m at a loss. Been trying to feel better for years. I have yet to find a doctor that will consider anything but levothyroxine. I’m currently taking 100 mcg. Thanks
My husband has the same symptoms of racing heart at night. He has had all stress tests done and told nothing appears to be wrong. He does not take thyroid medication. He is aware that other things can cause this to happen, such as alcohol. My unprofessional opinion is to look up what causes the heart palpitations and not to blame the thyroid medication. Both of us have health problems and it was quite by accident I found Dr. Childs advice on thyroid medicine, but he hits on information not found elsewhere. Hopefully, you can find the information you need. Keep digging!
So if too much thyroid hormone can cause palpitations, does that mean that too low a heart rate (bradycardia) is an indication one is not taking enough thyroid hormone?
My heart beat varies a LOT during the day depending on what I’m doing. It’s very responsive. Up when I’m exercising (with good oxygen saturation, steady beats), but can be 45 beats when resting reading a book. During sleep I believe it’s often in the 55-58 BPM range. Is that what is meant by HRV? (heart rate variability)?
I recall listening to your interview with Paul Robinson and you mentioned that your wife takes 50mcg dose at night. This is my third try on T3 and I was splitting it because I thought there’s no way you could take 50mcg all at once. You’d have a heart attack!!! So I finally took the jump and took the full dose close to bed, which is 50mcg at this time. My fitbit shows that my heartrate was slightly lower and the pattern was normal looking through the night on the one dose. When I was splitting the doses my heartrate pattern overnight was really sad looking.
Hi Jrborenz,
Good memory! My wife used to take between 25 to 50 mcg each day but we have successfully weaned her off and now she doesn’t take any. I’ve been meaning to write an article about that process but haven’t yet!
“we have successfully weaned her off and now she doesn’t take any. I’ve been meaning to write an article about that process but haven’t yet!”
Have you written that article yet? The inhibition to start taking thyroid meds is due to the burden or fear of having to be on them for life. Why such an epidemic of thyroid issues? And what is the overall root cause that can be addressed to correct with food, lifedtyle and temporary meds once it is corrected is what interests me.
Hi Grant,
I have not written that article yet but you should find some helpful information in this one: https://www.restartmed.com/do-you-have-to-take-thyroid-medication-for-life/
Hi I had a thyroidectomy back in 2016 due to a malignant tumour they also removed a parathyroid gland, i have been on a high dose of levothyroxine 150mg. I have just had my annual blood test and the doctors called me as they were concerned that maybe it would be more beneficial for me to lower my medication to.125mg as it could impact my heart and bone density when much older. I am 51. I do have what I can only describe as mild winded sensation in my chest. They are obviously wanting to avoid any complications later in my life but I was on a high dose to keep the cells from.reginerating again. Any advice would be most appreciated.
Hi I definitely have heart issues when meds are not right and very high cholesterol . What do you recommend to take for high cholesterol as I don’t want to take statins.
Hi Desley,
You’ll want to optimize your thyroid first to make sure your cholesterol problem isn’t related to your thyroid. In many cases, improving your thyroid can improve your cholesterol. You can learn more here: https://www.restartmed.com/hypothyroid-and-high-cholesterol/
I started taking 1/2 gr NDT years ago and was switched to Tirosint + Lio about 4 years ago. I ran an experiment over the course of 2 years with a very open minded Endocrinologist in Gilbert. She raised by Tirosint from 13mcg to 37mcg and Lio from 5mcg to 10mcg, even taking divided doses with all sorts of combinations, taking labs every 8 weeks. No matter what combo of T4 & T3 I took, my FT3 and FT4 remained very constant. What varied was my TSH (suppressed when more T4 was added). I don’t convert well. My RT3 goes up when I get more T4. For my entire life, my TSH, FT3 and FT4 have always been in the normal ramge. The problem is my FT3 is always at the lowest end of normal 2-2.2. So endo thinks I have NTIS, Low T3 syndrome due to another cause. She’s xrayed, and U/S my throid – all looks normal. I have horrid gut issues – IBS, SIBO, Candida, mold, HM. Have been working on them for years. Last year I started with palpitations. Dx was PSVT. Got a loop recorded implanted in April and now have documented Atrial Tach and a couple of episodes of Non Sustained Ventricular Tach. Tried 2 meds and failed (very low BP and more tach issues than without). Im on diltizem er now and will await my next dowload of heart data for this med trial to see if it helps. What I can tell you is that my body temp is low, my hair continues to shed and thin, I have brain fog, and many other hypo symptoms. At one point a year or so ago, I came off ALL thyroid meds for 3-4 months to see if my thyroid labs were affected. TSH went up to 2.1, FT3 2.0, FT4 1.1 – very little change. However, my A1c went up to 5.7 and my cholesterol went up to 201 (LDL used to be about 72, but then 101). So without thyroid meds, my glucose and cholesterol were deinitely affected. I’m 64, 5’8″, 123lbs, and eat very clean. Help! What could be the source of my low T3 syndrome? Can my Low FT3 be causing tachycardia? You always hear of hyperthyroidism and tach, but not hypo. Currently taking Tirosint 13mcg and Lio 5mcg.
Hi Sue,
You can learn more about the causes of low T3 in this article: https://www.restartmed.com/low-t3/
I’m in the UK and have had chest pains and symptoms of Hashimotos, including increasingly slow metabolism and goitre for decades (unconnected, but read on). I eventually had private tests for thyroid antibodies which showed they were high, as was my TSH, so Drs eveeeentually put me on Levothyroxine. Symptoms didn’t change much but I’m still on 50mg Levo as endocrinologist says my TSH has come down so he’s satisfied, so GP has had to give me hormones and laxitives, nightmare. However, endo did listen to my heart (which a cardiologist had refused to do, citing ‘indigestion’ after a number of normal ECG readings a while back), and found a heart murmur, so sent me for a heart scan which showed a bicuspid valve and bulging aorta, which will prob need open surgery at some point in the not too distant future – waiting to see a cardiologist, will have been a 30 week wait since diagnosis. Getting to the point… since I’ve been on T4 thyroxine for the past 9 months, my chest pains have been much less severe, and much more frequent. Explain that! I’m baffled.
Hi Rnightingale,
Chest pains aren’t always from the heart. You could be experiencing chest pain from acid reflux which was impacted by your thyroid medication or something similar.
I too have elevated cholesterol when more hypo . I’ve had a thyroidectomy and take synthroid only. Thoughts ?
Hi Lori,
You can learn more about the connection between high cholesterol and thyroid function here: https://www.restartmed.com/hypothyroid-and-high-cholesterol/
I’ve been on Tirosint for about a year and a half. I take 50 MCG a day my cholesterol is at its highest point the past 6 mos or so. I’m a bit scared. I switched thyroid doctors after figuring out on my own from reading on the internet that the cholesterol could be thyroid related. My new thyroid doctors added in five MCG of liothyronine and a selenium supplement, one daily. I go back for blood tests in October. They wanted to add cholestesure but I want to wait and see if these new additions help at all. I said no statin and then read that red yeast rice is the same as having a statin. Is there anything else I can do to get my cholesterol down? If I go for blood tests in October and it’s still just as high, what would you do?
Thank you! I really appreciate your blogs and help.
Hi Sherri,
I don’t have any resources on how to lower cholesterol right now but I will be writing an article on how to do just that in the coming weeks.
Hi Dr. Childs,
I’ve read your heart/cytomel articles but am still concerned about taking Cytomel even though I feel I really need it. As of 12/2/24, my T3 pg/mL was 1.5 ng/dl and rT3 was 27.1 ng/dl. I also have congestive heart failure and am currently taking Furosemide. My ejection fraction is only about 15%, maybe a little more. My diet is WFPB with no oil and low on salt and sugar. Besides getting 1000 – 2000 steps/day I do regular household jobs and lots of food preparation, sleep 7 – 9 hours/night, and try ti drink 64 oz. of fluid /day.
So, I am concerned about my heart even though I feel good, just don’t have the stamina I used too (77 years old). I feel a low dose of Cytomel would be beneficial for me, do you agree? (We are looking for a new doctor to help us with thyroid. I am currently on 75 mg Levothyroxine plus your daily vitamins and T3 conversion booster.)
Thank you for your insight and input!
Jane
Is there a connection between laking levothyroxine and osteoporosis? I had a thyroidectomy 15 years ago and have just been diagnosed with osteoporosis, despite being physically active, strength training, taking calcium, boron, vit D and K2, and eating a Mediterranean diet.
Hi Sarah,
Yes, I’m planning on doing an article/video on that topic in the near future. It will eventually be emailed out to my list but it will be posted to my blog first most likely.
I take levothyroxine because I had a complete thyroidectomy about 18 years ago. I have mostly genetic high cholesterol and a strong family history of heart disease, although so far my only issue is high cholesterol. I go yearly for blood work unless I feel like something is off with my thyroid – usually because of increased fatigue. I also have extremely high stress levels. I was wondering if my cortisol levels affect cholesterol and thyroid hormones (even synthetic ones!)? Should I be getting my cortisol levels checked regularly?
Hi Anne,
High levels of cortisol can impact cholesterol levels. Testing for cortisol isn’t always helpful/accurate, though, and you can learn more about that here: https://www.restartmed.com/cortisol-test/
After reading this article I realize that my hypothyroidism (Hashimoto thyroidism) is what is making my cholesterol high along with stress. I follow the diet for high cholesterol and instead of the numbers coming down they are going up and that worries me. I’m currently on Synthroid 75mcg and my doctor says my thyroid labs are good but not the cholesterol and it’s frustrating cause I don’t want to go on cholesterol medication.
Hi Lydia,
You can always try optimizing your thyroid function first to see how that impacts your cholesterol: https://www.restartmed.com/how-to-optimize-thyroid-medication/