Testosterone undecanoate (Undestor) is a revolutionary steroid because besides methyltestosterone is the only effective oral testosterone preparation. Testosterone is lost at oral doses of efficacy. It is absorbed through the portal vein and immediately inactivated by the liver. The Undestor (testosteronundecanoat active compound) is absorbed into the intestinal lymphatic system, without going through the liver. This fact causes its efficiency even with oral administration. Liver function is not affected. Testosteronundecanoat is a fatty acid ester - a natural androgen testosterone and the body is for the most part converted to dihydrotestosterone - a metabolite of testosterone. Therefore Undestor roll is bound aromatizes, ie. A very small part of the active substance can be converted to estrogen.