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Levothyroxine and Vitamins

Levothyroxine is the most common drug used to treat an underactive thyroid, a condition called hypothyroidism. It's a synthetic thyroid hormone replacement, taken in pill form once daily. Certain medications, minerals and foods can interfere with your body's absorption of levothyroxine. Taking your thyroid medication four hours before or after taking any other vitamins, supplements or medications will ensure that your body can effectively absorb levothyroxine.

Low Thyroid Function

Your thyroid gland is part of your endocrine system; it produces hormones that control the rate at which your body burns oxygen and calories -- your metabolism. If your thyroid doesn't produce enough hormones -- a condition called hypothyroidism -- you may gain weight, feel tired, experience a slowed heart rate and have an increased sensitivity to cold. Hypothyroidism is treated with replacement thyroid hormone supplements such as levothyroxine. About 5 percent of the population is affected by low thyroid production, and the condition affects women -- especially those over 50 -- much more often than men.


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Your thyroid produces two hormones, T3 and T4. Levothyroxine is a replacement for T4; your body can use T4 to synthesize the T3 hormone it needs, even if you have hypothyroidism. It's common to start with a very low dose of levoxothyrine and allow the drug to build in your system. It can take several weeks for levothyroxine to start to work. Levothyroxine is the generic name -- the drug is also sold as Synthroid, Levoxyl, Unithroid and Tirosint. Depending on what's causing your hypothyroidism, you may have to take levoxothyrine every day for the rest of your life.


Levothyroxine is designed to pass through your stomach and be absorbed in your intestines during digestion. Any substance that interferes with digestion can stop your body from fully absorbing this medication. This includes foods high in fiber and walnuts, soybean flour and cottonseed meal. Weight-loss drugs such as metofrmin and orlistat can also block levothyroxine. Vitamins that contain calcium and iron should not be taken at the same time, because these two minerals bind to levothyroxine in your digestive tract and decrease absorption of the hormone. Wait at least four hours after taking your thyroid medication to take any other pills that may interact with your levothyroxine.

Use and Other Interactions

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Take your thyroid medication with a full glass of water, on an empty stomach, first thing in the morning. Wait at least one hour before eating, especially high-fiber breakfast cereals. You will need periodic blood tests to check your thyroid levels. Too much levothyroxine can have serious medical consequences. In addition to vitamins, certain cholesterol-lowering medications, antacids, antidepressants, birth-control pills, seizure medications, blood thinners and diabetes medications can interact with levothyroxine. You may need a higher dose of levothyroxine to compensate, but do not adjust your medication without your doctor's approval.