Thyroid UK

Can thyroid medication impair existing thyroid function?

When bodybuilders take steroids their natural production of testosterone is shut down resulting in several unpleasant side-effects. I don't know how permanent this is and whether natural production starts up again some time after the drugs are stopped, but either way, is anything like this known to happen with existing thyroid function if supplementation were to fulfill requirements fully?

5 Replies


Well, thyroid meds won't cause your thyroid to shut down and stop working for ever, but they will cause your pituary gland to signal that less Thyroid Stimulating Hormone is required, so the message will not get to the thyroid to tell it to make hormones.

Does this help?




What would happen if the TSH went down to 0?


There are plenty of stories of people who, having been on full replacement doses of thyroxine, stop taking it for one reason or another, and turn out all right. Not exactly common but far from unknown.

However it is recognised that taking thyroxine will sometimes reduce the size of an enlarged thyroid. So I think your question is absolutely spot on - but the answer is a bit less dramatic and much less clear than for steroids.

All the best



Thank you Rod, much appreciated.


I have found the following studies which suggest that the hypothalamic-pituitary-thyroid axis returns to its previous state following thyroid hormone therapy.


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