Popular Supplements Contain Actual Thyroid Hormone


When you reach for an over-the-counter supplement to help your thyroid, you need to think twice. That supplement may contain actual thyroid hormone, like prescription thyroid drugs.

In 2011, researchers reported on a study of the actual thyroid hormone found as ingredients in the ten most popular over-the-counter (OTC) health supplements marketed as ''thyroid support" formulas.

The selected OTC thyroid supplements were evaluated for the presence of the key thyroid hormones thyroxine (T4) and triiodothyronine (T3).

The amount of T4 and T3 was measured separately for each supplement sample.

What the researchers found was surprising. Nine out of the ten most popular OTC thyroid supplements showed detectable amounts of T3 - the active thyroid hormone. The amounts of T3 ranged from 1.3 mcg to as much as 25.4 mcg per tablet. (T3 is sold in the United States as a prescription drug, known by the generic name liothyronine, and the brand name Cytomel.) 

Taken at the recommended dosage, five of the ten supplements delivered T3 quantities in excess of 10 mcg per day, and four delivered T4 quantities ranging from 8.57 to 91.6 mcg per day. (T4 is sold in the United States as a prescription drug, known by the generic name levothyroxine, and the brand names Synthroid, Levoxyl, and Tirosint.)  

Five of the supplements were labeled as containing bovine (cow) thyroid tissue, extract or concentrate. Among those five, one had no detectable level of T3 or T4; two contained T3 only, and two showed detectable amounts of both T3 and T4.

The researchers concluded that most of the OTC thyroid supplements studied contained clinically-significant amounts of T4 and T3 at levels that in some cases were similar to or greater than prescribed dosages of these hormones.

According to the researchers:

"This potentially exposes patients to risk of iatrogenic hyperthyroidism by taking easily accessible OTC supplements not requiring prescription. The current study results emphasize the importance of patient and provider education regarding the use of OTC herbal supplements and highlights the need for greater regulation of OTC supplements potentially dangerous to the public."

The term "iatrogenic hyperthyroidism" means hyperthyroidism caused by taking too much thyroid hormone from external sources, whether prescription thyroid drugs or OTC supplements.

What Should Thyroid Patients Know?

There are several important takeaways from this research that can significantly affect your health.

First, these supplements are delivering prescription ingredients as unregulated supplements. That means that here is no way to know how much and what type of thyroid hormone they may contain. (Note: the study did not list the brand names of the ten supplements studied.)

Second, if you are already taking a prescription thyroid drugs for your thyroid hormone replacement, taking an additional OTC supplement could cause you to become hyperthyroid, as a result of taking excessive amounts of thyroid hormone. It may be tempting to think that "hyperthyroidism would be better than hypothyroidism," but hyperthyroidism comes with debilitating and potentially dangerous symptoms, including anxiety, diarrhea, insomnia, and heart rhythm abnormalities, among others. Unchecked hyperthyroidism also poses a low but deadly risk of a potentially fatal condition known as thyroid storm. 

Third, you may be tempted to take these supplements because you feel undermedicated or that your prescription drugs aren't working.

 and hope that adding more thyroid hormone may cause weight loss, or improve energy. But note that many patients who become hyperthyroid due to overmedication actually report anecdotally that when hyperthyroid, they gained weight - or didn't lose weight. In addition, the combination of insomnia and anxiety resulting from the hyperthyroidism actually worsened rather than improved the fatigue for many.

Fourth, if you are among the patients who are unable to get diagnosed or prescribed regularly, you may feel that these OTC supplements could be a replacement for your prescription thyroid medications.

It's important to note that without knowing the ingredients and actual hormone content, it is virtually impossible to choose a supplement and dosage that will provide the right dosage of thyroid hormone necessary to resolve your hypothyroidism. And as noted, there is a risk that the supplement chosen may contain no hormone at all or an excessively high amount of hormone.

Finally, and most importantly, if you are hypothyroid and considering use of an OTC "thyroid support" supplement, you should discuss this with your health care practitioner, and be careful to use only those brands they recommend. This is the only way to avoid the risk of becoming overmedicated.


Kang, G.Y. "Thyroxine and Triiodothyronine Content in Commercially Available Thyroid Health Supplements," Abstracts of the American Thyroid Association Annual Meeting, 2011

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