Mesterolone is an anabolic steroid that goes by the brand names Mesviron 25 and Proviron 25. Mesterolone is taken orally in tablet form. It is part of a class of drugs known as androgens, or male hormones, and is usually take in conjuction with testosterone, an important male hormone. Mesterolone can be used to treat disorders in which the body does not produce enough male hormones naturally, or it can be used to enhance the already-normal levels of male hormones for muscle build-up. It does this by inhibiting estrogen production, increasing the potency of testosterone, increasing muscle density and hardness, and decreasing libido. It is said in other places to increase the libido, improve health, give a feeling of overall well-being and energy, and to restore youthfulness in adult men. Some doctors prescribe mesterolone for the symptoms of ale menopause, which men experience as testosterone levels decrease with age. It can also be prescribed for some types of sexual dysfunction, such as disinterest, impotency, and low sperm count.