When your body has enough testosterone, the brain does not send the luteinizing hormone (LH) signal to your testicles. This means you will not make any testosterone until your levels drop to below normal, causing the signal to return and stimulate production. Since you are getting testosterone from an outside source, your brain is most likely not sending that signal to your testicles. Over time, the adage of “use it or lose it” comes into play, and your testicles will shrink in size. The time and amount of shrinkage are different for every man.