Trenbolone is an androgen and anabolic steroid (AAS) of the nandrolone group, which itself was never marketed. Trenbolone is used in veterinary medicine to improve muscle mass and appetite. It works as a growth promoter, increasing feed efficiency and mineral absorption in cattle. Trenbolone ester drugs include trenbolone acetate and trenbolone hexahydrobenzylcarbonate. Trenbolone acetate has never been approved for use in humans, and therefore guidelines for human consumption do not exist. However, athletes and bodybuilders have been using trenbolone acetate as a physique- and performance-enhancing drug for decades. Some argue there are many benefits for bodybuilders using trenbolone acetate as an AAS. Unlike exogenous testosterone, trenbolone acetate does not cause fluid retention, so bodybuilders appear leaner; therefore, it is more commonly used during preparation for competitive events. Trenbolone acetate does not convert into an ooestrogenic metabolite; thus, there are no ooestrogenic side effects. Trenbolone enanthate is a commonly used AAS and lasts much longer than trenbolone acetate with intramuscular injection.