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What Are The Common Side Effects and Interactions of Thyroid Medication?

Published April 22 2013

Although it is important for many people with thyroid and autoimmune thyroid conditions to take medication to manage their symptoms, I think it’s safe to say that most people aren’t familiar with the side effects of these medications.  In addition, there can also be interactions with different medications and foods, and I figured it would be a good idea to discuss these as well.  I’m going to do this for both hypothyroid and hyperthyroid conditions.


What Does It Do: It’s a synthetic form of thyroid hormone that is typically used in people with hypothyroid conditions, as in these conditions the thyroid gland isn’t producing enough thyroid hormone on its own.  It can also be used in some cases to treat goiter.

Dosage: This of course can vary, as a lower dosage would be between 12.5 and 25 mcg, but some people can take doses as high as 200 mcg, and in rare cases higher doses than this.

Side Effects: Many people don’t experience side effects when taking synthetic thyroid hormone, although some people are sensitive to it, while for others it can be difficult for the doctor to get the correct dosage.  Many people don’t realize that the ingredients can include corn starch, lactose, and even artificial coloring (i.e. D&C Yellow #10) (1) [1]. Some people experience side effects such as hair loss, hot flashes, sleep problems, etc.  However, to be fair, some people will experience these same symptoms before taking thyroid hormone, and some will notice symptomatic improvement upon taking the medication.

Interactions: Synthetic thyroid hormone can interact with a lot of different medications, as well as nutrients, which is why most people will usually take it first thing in the morning on an empty stomach, and then will wait awhile before eating or taking anything else.  Some of the common nutrient interactions include calcium and fiber.  Quite frankly, there are too many interactions to list here, and so if you want more information I would visit the website www.drugs.com and click on “interactions”.

My opinion about this medication: I agree that many people with hypothyroidism and Hashimoto’s Thyroiditis need to take thyroid hormone to manage the symptoms, and some people do need to take thyroid hormone on a permanent basis.  The problem I have is that just about everyone with a hypothyroid condition is told to take synthetic thyroid hormone for the rest of their life, without looking into the cause of the condition.  For example, 90% of people with hypothyroidism have Hashimoto’s Thyroiditis, which is an autoimmune condition which results in destruction of the thyroid gland.  While this destruction of the thyroid gland might eventually make it necessary for some people to take thyroid hormone on a permanent basis, most medical doctors don’t do anything to address the autoimmune component, or other compromised areas of the body.

Armour Thyroid

What Does It Do: It’s a natural form of thyroid hormone that is taken by some people with hypothyroid conditions.  Whereas levothyroxine is synthetic T4, Armour Thyroid has both T4 and T3.  There are other forms of natural thyroid hormone, such as Nature-Throid.  Both forms are derived from porcine thyroid glands.  Natural thyroid hormone does require a prescription, and unfortunately, many medical doctors won’t prescribe this to their patients.

Dosage: The dosages are usually listed as grains.  For example, 1/2 of a grain is equivalent to 30 mg, and this would be equivalent to 50 mcg of levothyroxine.  The required dosage of course will vary from person to person.

Side Effects: Most people who are taking Armour Thyroid don’t experience side effects, although just as is the case with synthetic thyroid hormone, some people don’t do well when taking this and might do better taking Nature-Throid, or perhaps even synthetic thyroid hormone.   Armour and Nature-Thyroid both have different inactive ingredients, which is one reason why someone might do better on Nature-Throid, although many people do great when taking Armour.

Interactions: Just as is the case with synthetic thyroid hormone, natural thyroid hormone can interact with numerous medications, as well as foods, including calcium, fiber, soybean flour, and walnuts (2) [2].  So someone taking natural thyroid hormone will also want to take this first thing in the morning on an empty stomach.

My opinion about this medication: Although I do prefer natural thyroid hormone over synthetic thyroid hormone and wish more endocrinologists would be open to recommending it to their patients, both Armour Thyroid and Nature-Throid also don’t do anything for the actual cause of the condition.  And so while I realize that many people with hypothyroid conditions need to take synthetic or natural thyroid hormone, I of course feel that the underlying cause of the condition should be addressed.  This is true even for those people who need to remain on thyroid hormone for the rest of their life.

Methimazole and Propylthiouracil (PTU):

What Do These Do: These are both antithyroid medications, which are taken in hyperthyroid conditions.  They inhibit the enzyme thyroid peroxidase (3) [3], which is required for the formation of thyroid hormone.  They also both interfere with the conversion of T4 to T3.

Dosage: This will vary, as with methimazole, someone with a mild case of hyperthyroidism might take 5mg to 10mg per day.  Moderate to severe cases can require anywhere from 20mg to 60mg per day.  With PTU, someone with mild to moderate hyperthyroidism will usually take around 300mg per day in divided doses, and will take higher doses in severe cases of hyperthyroidism.

Side Effects: Some of the common side effects of both methimazole and PTU include hair loss, muscle or joint pain, swelling, itching or a minor skin rash, or an upset stomach.  Some people experience dizziness and headaches, although this doesn’t seem to be as common.  More severe side effects include a lowering of white blood cells, blood in urine or stools, or flu-like symptoms. Methimazole can also potentially lead to hepatotoxicity (4) [4], especially with larger dosages.  Although some people are sensitive to both of these medications, some people will react to methimazole but will do fine on PTU, and the reverse can be true as well.

Interactions: Although I have some patients who take methimazole who are also taking coumadin (warfarin), taking both of these together can cause someone to bleed more easily (5) [5].  As a result, most medical doctors will need to be careful with the dosages.  I have mentioned the herb Bugleweed in numerous articles and posts, as this herb has antithyroid activity, and therefore can help many people with hyperthyroid conditions.  However, one needs to be careful about taking both Bugleweed and methimazole at the same time, as taking high doses of both at the same time can cause someone to become hypothyroid.

My opinion about this medication: When unmanaged, the cardiac symptoms associated with hyperthyroidism can be dangerous.  While some people will take natural supplements and herbs to help manage the symptoms (Bugleweed, L-Carnitine, etc.), some people need to take something more potent, and as a result may need to take antithyroid medication to manage the symptoms.  I of course would prefer for people to take these drugs rather than receive radioactive iodine treatment.  But even though some people do go into remission when taking antithyroid medication, these drugs of course don’t do anything for the underlying cause of the condition.


What Does It Do: This is a beta blocker, and with hyperthyroidism and Graves’ Disease the goal is to help with the cardiac symptoms.  And so it can help with the increased heart rate and palpitations.  If someone has high blood pressure then it also can help with this  There are other types of beta blockers, and for the most part they work similarly.  I chose to discuss Propranolol because it’s the most common beta blocker prescribed for people with hyperthyroid conditions.

Dosage: For hyperthyroid conditions the dosage can range between 10mg and 80mg, and in some cases higher than this.  The dosage given usually corresponds with the persons cardiac symptoms.  For example, someone with a high pulse rate and severe palpitations will usually require a higher dosage than someone with mild palpitations and a pulse rate which isn’t too high.

Side Effects: Some of the less severe side effects of Propranolol include fatigue, insomnia,  nausea, stomach cramps, diarrhea or constipation.  Some of the less common, although more serious side effects, include feeling light-headed, fainting, shortness of breath, swelling of the ankles or feet, severe skin reaction, fast, slow, or uneven heartbeats (6) [6].

Interactions: Propranolol may interact with NSAIDs, calcium channel blockers, Xanax, Ambien, and other medications (7) [7].  Drinking alcoholic beverages might affect the absorption of propranolol.

My opinion about this medication: Just as is the case with antithyroid medication, some people do need to take beta blockers to help manage the symptoms.  I’m fine with people doing this, and if someone has a very high pulse rate it might be a good idea to take this medication, at least on a temporary basis.  For those looking for a natural alternative, the herb Motherwort can help to manage the cardiac symptoms in many people with hyperthyroidism and Graves’ Disease.  But once again, for some people this herb might not be strong enough to manage the symptoms.

In summary, while I’m grateful that medication is available to help people with hypothyroid and hyperthyroid conditions, I hate the fact that most medical doctors recommend medication without looking into the cause of the problem.  So yes, some people with hypothyroid conditions do need to take synthetic or natural thyroid hormone, while some people with hyperthyroid conditions need to take antithyroid medication and/or beta blocker.  However, if one needs to take these medications the goal still should be to address the cause of the condition.