Clinical data
SynonymsTHG; The Clear; 17α-Ethyl-18-methyl-δ9,11-19-nortestosterone; 17α-Ethyl-18-methylestra-4,9,11-trien-17β-ol-3-one
Routes of
By mouth, intramuscular injection
Drug classAndrogen; Anabolic steroid; Progestogen
Legal status
Legal status
CAS Number
PubChem CID
Chemical and physical data
Molar mass312.46 g/mol
3D model (JSmol)
 NYesY (verify)

Tetrahydrogestrinone (THG), known by the nickname The Clear, is a synthetic and orally active anabolic–androgenic steroid (AAS) which was never marketed for medical use.[1][2] It was developed by Patrick Arnold and was used by a number of high-profile athletes such as Marion Jones and Dwain Chambers.

Non-medical uses

THG was developed completely in secret by Arnold as a designer drug, on the basis that doping testers would be unlikely to detect a totally new compound. Arnold developed a chemical similar to two obscure steroids marketed by BALCO, norbolethone and desoxymethyltestosterone, which had been reported in scientific literature but never entered mass production, and the banned anabolic steroids trenbolone and gestrinone, the latter of which was used to synthesize it.[3]

In 2003, whistleblower Trevor Graham passed a spent syringe containing a small amount of the drug to the United States Anti-Doping Agency. This was then transferred to the research group of pharmacologist Don Catlin, who identified the drug using mass spectrometry techniques and gave it its present name.[4][5]

THG has never been fully tested for safety and has never entered legitimate medical use, although some studies have been made of its properties.[6] A synthesis was devised to ensure a source of material for comparison and it was scheduled by the Food and Drug Administration (FDA) in 2005.[7][8] Concerns have also been raised about its potential use in animals such as in horse-racing.[citation needed]

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