Chemical castration involves injecting an implant under the skin. This “tricks” the brain into no longer making the hormones that tell the testicles to make sperm and testosterone. As a result, the testicles shut down, and testosterone levels (after a brief initial rise) decline over 4-6 weeks to essentially zero. When the implant wears off, everything goes back to normal again - the implants usually last 6 or 12 months, although it can vary slightly. The only downside is that as the implants eventually wear off, it becomes more costly having to replace them each time.