Is it Safe to Take Thyroid Hormones for Weight Loss?

What are thyroid hormones?

Thyroid hormones are approved by the US Food and Drug Administration (FDA) to treat hypothyroidism, the condition that results when the thyroid gland does not secrete enough hormones. Hypothyroidism can occur due to problems with the endocrine system or following thyroid removal, which might be necessary to treat thyroid cancer. Symptoms of hypothyroidism include fatigue, weight gain, thin hair, and cold intolerance. Hypothyroidism is diagnosed by blood testing and often requires lifelong treatment with thyroid hormones taken by mouth daily.

Prescription thyroid hormones work by replacing the natural hormone that is not being made because the gland is either not working properly or has been removed. The most commonly prescribed thyroid hormone is levothyroxine (Synthroid). Thyroid hormones increase the body’s metabolism, which can cause weight loss. 

Can thyroid hormones promote weight loss?

Since thyroid hormones can increase the body’s metabolism and promote weight loss, there has been interest in using them as a diet aid. Some people use prescription thyroid medications for this reason, but thyroid hormones are sometimes found as illicit additives in over-the-counter weight-loss supplements.

Do thyroid hormones have to be prescribed?

Unlike tightly regulated prescription medications, over-the-counter weight-loss products can contain several different hormones of variable potency. Since over-the-counter weight-loss products are dietary supplements, they are not supposed to contain prescription medications such as thyroid hormones.

What are the side effects of taking thyroid hormones?

The human body is very sensitive to changes in thyroid hormone concentrations. Taking too much of a thyroid hormone can result in hyperthyroidism. People with hyperthyroidism can have a rapid heart rate, anxiety, heat intolerance, and stomach discomfort. In severe cases, confusion, elevated body temperature, and abnormal heart rhythms are possible. If thyroid hormone is taken in excess for a prolonged period of time, heart failure and osteoporosis (weakening of bones) can occur. Thyroid storm is a rare but life-threatening condition that can occur. When this condition causes death, it is usually due to heart failure or multiple organ failure. 

People should not take prescription thyroid hormones unless they are under the care of a doctor for the treatment of hypothyroidism. People should not take over-the-counter weight-loss supplements that contain thyroid hormones. If unwanted or unexpected symptoms occur after taking over-the-counter weight-loss products, seek medical attention as soon as possible.

What should you do if you have an adverse reaction to thyroid hormones?

If you suspect someone has taken thyroid hormones inappropriately or is having an adverse effect to a thyroid drug or weight-loss supplement, do not make the person vomit. Get an immediate personalized recommendation online or call Poison Control at 1-800-222-1222. Both options are free, confidential, and available 24 hours a day.

Maryann Amirshahi, PharmD, MD, MPH, PhD
Medical Toxicologist

Revised William G. Troutman, PharmD
Professor of Pharmacy Emeritus 

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