It's different with different people. I know guys who can take boat loads of tesosterone, and we all know that tesosterone has been known to shut down your own tesosterone production. Yet these guys, it doesn't. And then there are men like me, who took only small amounts of it, and was forced to stay on it for life because just that small amount of testosterone suppression, was enough to permanently effect my natural level. I once stayed off of the testosterone injections for four years, and though my level did return to functional, it never did return to what it was before.

I, for one, think chemical castration is reversible.

I was chemically castrated for 59 months, almost 5 years. During that time, my prostate, which had been enlarged, atrophied to smaller than normal. PSA went to zero, as did semen production. I only went off Cypro to avoid possible drug interaction questions while being treated for cancer. In the 18 months that followed, I felt that my sexuality returned almost to normal. PSA went back up to 3.1 and semen volume returned to an abnormal 5-8 cc. During this time my doctor measured my testosterone level at 691 ng/dL. That's about average for a 25 y.o. ; I'm 65.

I then went back on for 5 months, and have been off for the last 5 months. Again, PSA, semen volume, and T level have returned to normal. I feel the effects of testosterone much more strongly now, maybe because I was testosterone-free for so long.

Although I think T will rebound relatively quickly after discontinuing cyproterone, prostate size, semen volume, and sexual desire, which is caused by the engorgement of the semen producing glands will take longer as the seminal vesicles and prostate grow back to normal size.

I think MrT was close when he mentioned HCG. If you read some of the bodybuilding forums where it is common for them to take steroids which tend to shut down the testicles, HCG is frequently used (temporarily) after a cycle of steroid use to get the testicles working again. But here the common process is just to stop the antiandrogen and hope the testicle will magically start working again. Maybe that works in some cases, maybe it doesn't. But certainly using some HCG or other substances to jump start the testes after chemical castraion would increase the chances of testosterone being produced again.

I have no personal experience here. I was chemically castrated for over 2 1/2 years and only stopped when my surgery was arranged. But I do follow other forums where testosterone levels are a major concern.