Tetrahydrogestrinone, also known as THG or less technically The Clear, is an anabolic steroid chemically similar to gestrinone and trenbolone. THG is a potent agonist for androgen receptors, estimated to be at least 10 times as potent as the comparable steroid trenbolone, meaning that it builds muscle and burns fat extremely quickly at very small dosages (about 5mg or "just a few drops under the tongue"). Unfortunately for the people using it, it is also an extremely potent agonist for progesterone receptors, so it's also likely to halt natural testosterone production, leading to significant side effects.
It was invented by Patrick Arnold in the late 1990s with funding provided by Victor Conte's company, Bay Area Laboratory Co-operative. BALCO was a legitimate distributor of dietary supplements on the surface, but was also involved in the distribution of various illegal steroids to professional-level coaches and athletes. THG was intended to be another one of their designer drugs, which could be used by athletes to increase physical performance while still fooling anti-doping tests. It worked for a while until a disgruntled Trevor Graham, sick of being beaten by BALCO-enhanced players, sent a sample of the drug to the U.S. Anti-Doping Agency. Within a few years the USADA developed a test that responded to THG, limiting its usefulness and effectively removing it from the professional sports scene. It was classified as a Schedule III controlled substance by the Food and Drug Administration in 2005.
Although inventions like THG have landed him in prison a few times, Patrick Arnold insists that what he does is admirable. He was bullied at a young age due to his "nerdy" obsession with chemistry, and as a result became obsessed with self-improvement. During high school he worked out extensively and created his own protein bars, but was frustrated by the lack of visible muscle mass. After sampling steroids for the first time in university, he devoted his life to creating what he calls "performance enhancers", and insists that his drugs have been "given a bad rap". Most people disagree.
[S]ome steroid precursors are clearly outside the scope of the dietary supplement definition and are subject to regulation as drugs because they are intended to affect the structure or function of the body. For example, FDA considers tetrahydrogestrinone ... a new drug under [the Food, Drug, and Cosmetic Act]. Our analysis demonstrates that this is a purely synthetic, non-naturally occurring, highly potent anabolic steroid. It is a designer steroid in the truest sense. --John M. Taylor, Associate Commissioner for Regulatory Affairs
Notable athletes who have abused tetrahydrogestrinone include Barry Bonds, Jason Giambi, and Dwain Chambers. Tim Montgomery and Marion Jones have lost medals over their use of THG.
The media frenzy created after the discovery and listing of THG went down in history as the BALCO Scandal. The scandal caused Major League Baseball to strengthen its policy against performance-enhancing drugs and, obviously, destroyed BALCO as a company. However, Victor Conte has since founded a new company called Scientific Nutrition for Advanced Conditioning, which allegedly does not deal illegal drugs like his old company did.