In a word,
TRT should not CAUSE “permanent” infertility. The key word here is “permanent”. And normally
TRT won’t even cause temporary infertility but it may in some cases.
TRT does reduce testicular function as having normal, or above your personal normal, levels of T will cause your Hypothalamus-Pituitary to reduce LH and FSH excretion. This in turn causes your Testicles to slow down production of T and Sperm. Depending on your condition this may cause infertility or it may just reduce your fertility from your normal levels.
Now, if you have primary hypogonadism (meaning a testicular problem resulting in low T) then it is possible that your testicles will continue to degenerate in function while you’re on
TRT and may eventually lead to infertility. Of course if you are in this situation then eventually you would probably become infertile regardless of whether you were on
TRT or not. It’s just that if you were in this situation you would become infertile sooner than if you were not on
TRT.
In my situation it is suspected that since I’ve had two hydrocele operations on both testies, and one atrophied testicle, that my hypogonadism is at least partially caused by a primary condition. Since I don’t know if my condition is degenerative I decided that it would be best if I banked some sperm while I’m fertile just as insurance against possible long term infertility. So before starting
TRT I banked some sperm which I hope I will never need to use but at least I know it’s there if I do need it.
More than likely I will not become infertile but as my brother (who’s an electrician) says, “it’s better to be looking at it then looking for it.” Of course he was talking about electrical cable but it works for sperm too. :-)