Because of their ability to reduce risk of gynecomastia (abnormal growth of breast tissue in males) and enhance recovery of natural testosterone production after a cycle, use of antiestrogens such as aminoglutethimide (Cytadren) and clomiphene (Clomid) has become popular in bodybuilding. Antiestrogens also can reduce bloating associated with anabolic/androgenic steroid use, and may avoid health risks associated with elevated estrogen levels. Medically, the drugs are used not only for treatment of breast cancer but also for improvement of fertility in both men and women, and occasionally for increasing testosterone levels in men such as endurance athletes with low testosterone. There are two categories of antiestrogens: aromatase inhibitors and receptor blockers. Both shall be considered here.
