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Questions about Generic Thyroid Medicine

Q. I have been on thyroid medication for the past year. Last fall I noticed my hypothyroid symptoms returning: fatigue, muscle cramps and stiffness after walking just a mile of my usual three-mile walk. I also felt extremely cold, while others were comfortable.

When I saw my doctor and told him about my symptoms, he checked my thyroid levels and gave me a month’s supply of Synthroid to tide me over. I had been taking generic levothyroxine.

A measure of thyroid function, my TSH level, was 3.7 on the generic. On Synthroid my TSH was 2.5 and all my symptoms disappeared even though the dosage is the same (50 micrograms). If there is such a difference from one brand to another, how can dosage be regulated properly?

A. The FDA maintains that all levothyroxine formulations (Levoxyl, Synthroid, etc) are identical. Physicians who specialize in treating thyroid disorders (The Endocrine Society) disagree. They worry that patients are put at risk when they are switched between branded or generic thyroid medicines.

For more information about symptoms, side effects, interpreting lab tests and treatment strategies we offer our Guide to Thyroid Hormones.

People who get switched need thyroid function tests afterwards. Doses may also need to be adjusted for seasonal variation (lower TSH during the summer).

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About the Author
Terry Graedon, PhD, is a medical anthropologist and co-host of The People’s Pharmacy radio show, co-author of The People’s Pharmacy syndicated newspaper columns and numerous books, and co-founder of The People’s Pharmacy website. Terry taught in the Duke University School of Nursing and was an adjunct assistant professor in the Department of Anthropology. She is a Fellow of the Society of Applied Anthropology. Terry is one of the country's leading authorities on the science behind folk remedies..
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