THG (Tetrahydrogestrinone)

THG (tetrahydrogestrinone), often referred to as "The Clear", is an anabolic-androgenic steroid (AAS) developed by Patrick Arnold. This compound is considered a designer drug closely related to the banned anabolic steroid trenbolone and gestrinone. It is most known for being associated with doping by Olympic and professional athletes, and specifically the BALCO scandal.

Gestrinone vs THG

Fig 1. Gestrinone vs THG

Table of Contents

BALCO Scandal

The Bay Area Laboratory Co-op (BALCO) was an American company led by Victor Conte. Patrick Arnold provided Conte with several doping compounds that were then distributed to athletes mostly in the US, and Europe. As a result, it was discovered that THG (the main BALCO drug) was one of the most common compounds used for doping. The most well known athletes were MLB and NFL stars, which included: Barry Bonds, Bill Romanowski, as well as Olympic athletes Kelli White and Marion Jones. In all, well over 35 athletes from cycling, to boxing, to even Judo, were found to be customers of BALCO at one time. Kelli White admitted to using THG, and she was disqualified from the Olympics. Patrick Arnold was sentenced to 3 months in prison for his role in the BALCO scandal.

balco labs

Fig 2. BALCO

History and Patrick Arnold

Patrick Arnold is an American organic chemist, and amateur bodybuilder; dubbed the "father of prohormones" for his creating and introducing, several designer drugs and compounds to the market. Arnold became fascinated with steroids after using a bunk version of methyltestosterone (given to him by a buddy at his gym), which added 10 pounds of lean muscle on his frame in a short time; thereafter, he began studying the effects of AAS.

In 1996, he befriended Dan Duchaine (another 'founding father' of the steroid industry), who helped him expand his research and network all throughout the late 90's into the next decade. Arnold then introduced '1-androsterone' (andro) to the market, but he blew a marketing opportunity after the Mark McGwire scandal. This was mainly because he was not selling andro directly, but as part of his supplements.

Arnold wanted to produce compounds that were not detectable, and after being approached by Victor Conte (owner of BALCO), and supplying him with norbolethone, he decided to switch to THG to throw off scrutiny from drug testers in 2001.

How THG works

THG was developed for one reason, to give athletes an edge. When it reaches the nucleus of a cell, it binds to the androgen receptor at the ligand binding pocket; turning on anabolic and androgenic functions. Tetrahydrogestrinone is potent because of its high affinity to the androgen receptor.

Avoiding detection

Patrick Arnold developed THG to avoid detection via the catalytic hydrogenation of gestrinone (an anabolic steroid). This worked, until a disgruntled track coach (Trevor Graham) mailed the world doping agency a sample of the substance, which helped blow the lid off the BALCO scandal. It followed by an end to athletes getting away with using it without detection.

Effects as a performance enhancing drug

THG is a very strong and effective steroid which has several benefits.

  • Increased lean muscle mass
  • Increased strength
  • Faster recovery
  • Reduced catabolism

Both female and male athletes used THG to make them bigger, stronger, and give them an edge over the competition in a wide variety of sports. They did not have to worry about excess water weight because of the lack of aromatization into estrogen in the body. Many steroids that do aromatize will slow down athletes who will end up carrying excessive water weight.

Side effects

Any time an athlete is using AAS, they can expect suppression of the pituitary glands. LH and FSH will drop to near 0 (zero) and the testes no longer produces testosterone. Therefore, it's important to have a post cycle therapy in place. THG suppresses severely because it is 7x more potent then progesterone itself.

THG does not aromatize, so estrogen related side effects wouldn't be a problem; however, this does not mean progestin type side effects wouldn't be a problem. A decrease in libido, from elevated prolactin, would be very possible. Since gains were so fast, an increase in blood pressure, heart strain, other organ strain would of been very common.

THG was used by females as well, and some virilization was possible, which includes enlarged clitoris, deepening voice, and facial hair.


As mentioned above THG was designed to be solely used by athletes for performance enhancing. There has never been research done for any other medical purpose; however. we can assume if it had been done, it would of been a poor choice as a muscle wasting steroid because of it being a progestin. It will likely suppress the immune system because it has many trenbolone traits.


THG was given in a suspension of oil and placed under the tongue. A very small amount was all that was necessary and athletes were told to take 5-10mg per day.


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