What is Proviron? Proviron or Mesterolone, is  anabolic-androgenic steroid (AAS). Proviron’s unique properties and its role within both medicinal applications and the bodybuilding community merit an in-depth exploration to understand its uses, benefits, risks, and the controversy that surrounds its non-prescribed use. Proviron was designed to treat testosterone deficiency, reduced libido, fatigue, decreased muscle mass.