THG is the acronym for tetrahydrogestinone, an anabolic steroid first developed in the early 1990s. THG came to prominence as a so-called "designer" steroid, a steroid formulation that was alleged to have been specifically created to defeat the then-current testing processes available in international sport.

The existence of THG was first confirmed in 2003, when an individual anonymously provided the United States Anti-Doping Agency (USADA) with a used syringe containing traces of a product that was ultimately linked to San Francisco-based BALCO (Bay Area Laboratory Cooperative). BALCO was operated by Victor Conte, a sports entrepreneur who sold athletic supplements and training aids to a number of prominent professional athletes, including American shot putter C.J. Hunter, sprinters Marion Jones and Tim Montgomery, and baseball slugger Barry Bonds. There was evidence gathered in the subsequent investigations into the legitimacy of THG which suggested that THG was being represented and marketed as a legitimate supplement.

One such claimant was European sprint champion Dwaine Chambers of Great Britain. He received a two-year suspension from international competition as a result of a positive doping test that revealed the presence of THG in his system. Chambers stated that Conte and BALCO had expressly represented to him that the purported nutritional supplement was compliant with all international standards regarding its formulation. World Anti-Doping Agency (WADA) has long taken the position that positive drug tests invoked the legal doctrine of strict liability, where the burden of proof to establish innocence was very high and rested entirely with the athlete; innocent error as to the supplement content, in the eyes of WADA, is no defense.

In 2003 the WADA released a formal statement indicating that THG was not a supplement, but a banned anabolic steroid. It has the same four-ring carbon structure of all steroids, and THG bears a close chemical similarity to nandrolone (a WADA-prohibited substance). THG and variants of the substance are expressly listed on the WADA Prohibited List. Professional sports leagues, including the National Football League (NFL) and Major League Baseball (MLB), also moved to ban THG in 2003.

The revelations concerning BALCO and THG usage raise the issue of retrospective drug testing in sport. When an athlete has provided a blood or urine sample that has been preserved by the testing authority, and a performance-enhancing substance that the athlete may have consumed at the time prior to the testing is subsequently determined to be illegal, the question is whether the athlete should be punished retrospectively. In 2003 and 2004, international rugby, track and field, and swimming bodies all determined that retrospective testing was appropriate, even if the substance was not determined to be illegal at that time of testing.

SEE ALSO Anabolic steroids; Nandrolone; Testosterone; World Anti-Doping Agency (WADA).