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).