17a-dimethyl-bol (commonly known as 17α-methyl-dihydrotestosterone or methylated anabolic-androgenic steroids such as methasterone, superdrol, or methyltestosterone) is a synthetic anabolic steroid used primarily in bodybuilding to promote muscle growth, increase strength, and enhance physical performance. The use of 17α-alkylated oral anabolic steroids in bodybuilding is supported by scientific evidence, as these compounds have been demonstrated in controlled studies to significantly increase muscle mass and strength in both clinical and athletic populations. The "17a-methyl" modification makes these steroids orally bioavailable by preventing rapid hepatic metabolism, thus allowing effective oral dosing.

Multiple studies from the mid-20th century onward have documented the anabolic effects of 17α-methylated steroids, including increased nitrogen retention, protein synthesis, and muscle hypertrophy. These compounds were originally developed for clinical uses such as treating cachexia, hypogonadism, and certain anemias, but their potent anabolic properties led to widespread non-medical use among athletes and bodybuilders.

However, the use of 17a-dimethyl-bol and similar compounds carries significant risks, including hepatotoxicity (liver damage), adverse lipid profile changes, and suppression of natural testosterone production. Because of these side effects and the potential for abuse, such compounds are controlled substances in many countries and are generally not recommended for non-medical use.