Levothyroxine & Soy

Levothyroxine is a synthetic thyroid hormone used to treat people with hypothyroidism. The way this medication and similar drugs work in your body may be affected when you eat certain foods -- and soy is one of them. Mayo Clinic endocrinologist Todd B. Nippoldt states that if you take levothyroxine, you don't have to eschew soy completely. However, you should make sure that you take levothyroxine several hours before you consume soy foods.

More About Levothyroxine

Levothyroxine is the standard treatment for hypothyroidism caused by Hashimoto's thyroiditis, removal or radiation of the thyroid, or treatment for hyperthyroidism that renders the gland nonfunctional. If your doctor has prescribed levothyroxine to treat hypothyroidism, this is typically a lifelong commitment, according to MayoClinic.com. Concerns have been raised that soy foods worsen hypothyroidism. However, Nippoldt explains that soy may affect how well your body absorbs levothyroxine.

Soy Study

Foods to Avoid When Taking Thyroid Medication

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Results of a review examining the effects of soy on synthetic thyroid replacements was published in the March 2006 issue of "Thyroid," the official journal of the American Thyroid Association. Researchers at California's Loma Linda University examined 14 clinical trials to ascertain soy's influence on healthy adults and people with hypothyroidism. With the exception of one trial, researchers noted that all others showed no negative effects of soy or its isoflavones on thyroid function and concluded that there's no reason for people with hypothyroidism to avoid soy. They went on to state that theoretically, soy could exacerbate hypothyroidism in people whose condition was caused by low iodine intake. People who consume soy should therefore make sure they get enough dietary iodine.


Levothyroxine is usually taken a half hour to an hour before your first meal of the day with a large glass of water to make sure that your body absorbs it properly. Nippoldt suggests waiting four hours after you take your medication before you eat soy foods. He further states that there's no special diet for people with hypothyroidism that includes or excludes certain types of foods.

Other Information

Drugs & Foods to Avoid for Hypothyroidism

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Dietary fiber can also affect the absorption of levothyroxine. Other foods, supplements and medications to avoid taking at the same time include cottonseed meal, walnuts, iron and calcium supplements, multivitamins with iron, antacids and medications used to treat ulcers and high cholesterol. According to the National Center or Complementary and Alternative Medicine (NCCAM), soy foods are safe for most people and may even reduce high cholesterol slightly when you make them a part of your diet. Although soy supplements are sometimes used to address symptoms of menopause, NCCAM indicates that there's no solid evidence to support them for this use. If you have hypothyroidism and have questions about soy foods, talk to your treating physician. Always consult your doctor before using any type of dietary supplement to address your health concerns.