Tetrahydrogestrinone (THG) is an anabolic steroid that was specially designed so as to make it undetectable under normal drug testing.

The drug was made public when the United States Anti-Doping Agency was contacted by an anonymous athletics coach who claimed that several top athletes were using THG. The same coach subsequently provided the USADA with a syringe containing THG, which the USADA then used to develop a test for the substance.

The USADA identified the Bay Area Laboratory Cooperative, an american nutritional supplement company, as the source of THG.