Among athletes, HCG is used to stimulate natural testosterone production during or after a steroid cycle which has caused natural levels to be reduced. Stopping a steroid cycle abruptly, especially when endogenous androgens are absent, can cause a rapid loss in the athlete's newly acquired muscle. When HCG is used to stimulate natural production, a notably pronounced crash may be avoided. Pregnyl HCG is always packaged in 2 different vials,one with a powder and the other with a sterile solvent. These vials need to be mixed before injecting, and refrigerated should any be left for later use.