Proviron (Mesterolone) 25mg is an anabolic and androgenic steroid used to treat certain sexual problems. It is also used by athletes to increase strength and muscle mass. Proviron 25mg is a tablet taken orally and typically comes in packs of 50 tablets. It works by counteracting the effect of the estrogen hormone, which can result in increased libido and improved physical performance. Proviron 25mg should be taken with food and not taken more than 4 times per day. Side effects include headache, nausea, changes in sexual function, mood swings, and changes in hair or skin.