Tetrahydrogestrinone (often referred to as THG or The Clear) is an anabolic steroid. It has affinity to the androgen receptor and the progesterone receptor, but not to the estrogen receptor. The drug has been considered a designer drug, closely related to the banned anabolic steroids gestrinone and trenbolone, and was banned by the Food and Drug Administration (FDA) at the end of 2003.


Structure-activity relationship studies report that the potency of the drug is outstanding, surpassing, on a milligram per milligram basis, every known synthesized or commercial available anabolic steroid at the time of its development. It is a highly potent agonist for the androgen and progesterone receptors, around 10 times more potent than the comparison drugs nandrolone or trenbolone, but with no estrogenic activity. It has been found to bind to the androgen receptor with similar affinity to dihydrotestosterone and produces growth of muscle tissue.

Side effects

Side effects from prolonged use are likely to include infertility in both men and women, as well as other steroid side effects such as acne and hirsutism. Unlike most other anabolic steroids, THG also binds with high affinity to the glucocorticoid receptor, and while this effect may cause additional weight loss, it is also likely to cause extra side effects such as immunosuppression that are not seen with most other steroids.


For a time, THG was considered the drug of choice for safe and "invisible" world record breaking in athletics, being used by several high profile gold medal winners such as the sprinter Marion Jones, who resigned from her athletic career in 2007 after admitting to using THG prior to the 2000 Sydney Olympics, where she had won three gold medals. It has also been used by banned British athlete Dwain Chambers.

THG was developed by Patrick Arnold for the Bay Area Laboratory Co-operative (BALCO), an American nutritional supplement company. The company manufactured the drug through palladium-charcoal catalyzed hydrogenation from gestrinone, a substance used in gynecology for treatment of endometriosis.


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