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Can thyroid supplements be taken with food, vitamins, iron, or other minerals?

Thyroid supplements containing levothyroxine (brand names Synthroid, >Levothroid, and >Levoxyl) work best when taken on an empty stomach, at least one hour before or two hours after meals. This helps to increase the amount of drug that gets into the body and allows it to work as well as possible. In addition, thyroid supplements should be taken at the same time every day. Many people find this is easiest before breakfast.

Levothyroxine interacts with minerals such as iron, calcium, and magnesium, which lower the activity of thyroid medicine. Many antacids contain magnesium and aluminum, so avoid taking them when you’re on levothyroxine. If you take iron-containing products such as multivitamins with iron, make sure you do so at least two hours before or after you take your thyroid medication. If you take calcium, make sure there’s at least four hours between taking the two kinds of medications.

Be sure to notify your doctor or pharmacist regarding any prescription, over-the-counter or herbal medicines you are taking.

Sources:
Micromedex® Healthcare Series. Thomson Micromedex, 2006.
Drug Facts and Comparisons, Facts & Comparisons, 2006.

This answer prepared 7/24/2000.
This information updated 12/6/2006.