Does synthetic T3/T4 shutdown your thyroid gland?

[question]

Hi,
I wonder if synthetic T3 or T4 shutdowns your thyroid gland/HPTA similar to how testosterone shutdowns the testicles/HPTA?

On first hand it should do, since it also works through negative feedback? But I rememeber reading that it dosen't and studies showing people going off years/1-2 decades of thyroid replacement without any negative effects on thyroid production?

 

[ERO]

I have read that while it does suppress natural thyroid production while you are using it, it is only temporary. I found a reference to a study done in the 1950s.

An early study that looked at thyroid function and recovery under the influence of exogenous thyroid hormone was undertaken by Greer (2). He looked at patients who were misdiagnosed as being hypothyroid and put on thyroid hormone replacement for as long as 30 years. When the medication was withdrawn, their thyroids quickly returned to normal.


Here is a remark about Greer's classic paper from a later author:




"In 1951, Greer reported the pattern of recovery of thyroid function after stopping suppressive treatment with thyroid hormone in euthyroid [normal] subjects based on sequential measurements of their thyroidal uptake of radioiodine. He observed that after withdrawal of exogenous thyroid therapy, thyroid function, in terms of radioiodine uptake, returned to normal in most subjects within two weeks. He further observed that thyroid function returned as rapidly in those subjects whose glands had been depressed by several years of thyroid medication as it did in those whose gland had been depressed for only a few days" (3)