Tetrahydrogestrinone is a designer steroid used only by elite athletes. There were only a very small number of athletes who knew about, and had access to THG. THG was created by modifying two other known steroids, trenbolone, and gestrinone. Trenbolone has become one of the most popular steroids on the black market over the last couple years. Gestrinone (Dimetriose, Florizel) is used for treating endometriosis. The modifications made the drug undetectable in steroid tests, which is the reason for all the current hype on "THG". Tetrahydrogestrinone, no one is certain how long this drug has been used, but tests are now being down on urine samples from the 2002 olympics.
There is nothing special about Tetrahydrogestrinone. The only reason it is getting so much attention is because it was undetectable in steroid testing. Trenbolone alone, which THG was created from, is a strong steroid. However THG is much more toxic. Gestrinone was modified at the 17a-position which then made THG an oral steroid. It was used by placing the liquid under the tongue, and allowing it to absorb. This modification made the drug a 17aa steroid, which makes it a lot more toxic on the liver than other injectable anabolic steroids.
There you go bro!