Human growth hormone, the elephant-maker
Human growth hormone (also known as hGH or HGH) first came into popularity as a as a doping agent when it was recommend in Dan Duchaine's 1982 "Underground Steroid handbook." California, where the book was published, was the first state to see widespread use of the drug.
Despite the fact that hGH has been used by athletes in many different sports since then, some recent studies have not been able to show that it actually can improve the athletic performance of professional male athletes. Nonetheless, many athletic societies ban the use of hGH, and for Americans it is legally available only by prescription. It does have medical uses, in that it stimulates the growth, cell reproduction, and cell regeneration of humans and, indeed, other animals. It is because of this wide applicability that the word human is often dropped completely, and the generic term "growth hormone" used.
When abused, this hormone can cause the body to overdevelop in a disfiguring manner. This, coupled with the recent evidence showing that it provides male athletes with no actual benefit, seems a good reason to generally avoid its non-medical use.