Methylstenbolone, known by the nicknames M-Sten, Methyl-Sten, and Ultradrol, is a synthetic and orally active anabolic–androgenic steroid (AAS) and a 17α-methylated derivative of dihydrotestosterone (DHT) which was never introduced for medical use.
It is a designer steroid and has been sold via the internet marketed as a dietary/nutritional supplement and is said to be a mass-building prohormone that helps users gain size and strength without sacrificing definition.
Methylstenbolone has been ruled by the FDA to no longer be a legal dietary ingredient, and thus supplements are no longer able to be sold.