Nolvadex is a brand name for the drug tamoxifen citrate, a nonsteroidal agent which demonstrates potent antiestrogenic properties. These antiestrogenic effects are due to its ability to compete with estrogen for binding sites in target tissues such as in the breast. Medically, the effects of this drug make it very useful in breast cancer patients. Male bodybuilders however, find this drug very effective in combating gynocomastia (female breast tissue development). Gynocomastia is caused by excess estrogen in the male body. In the steroid user, this happens when anabolic steroids "aromatize" into estrogens. This is not as odd as you may think, structurally these hormones are very similar. So with Nolvadex competing for and occupying estrogen receptors, the buildup of tissue is greatly reduced and often avoided. It should be noted that Nolvadex also seems to slightly reduce to gains made during a steroid cycle. Some believe estrogen plays a role in keeping androgen receptors open. This may explain why Nolvadex would slightly hinder gains. Regardless of this effect Nolvadex is the most popular anti-estrogen used by athletes and many people swear by it. One should remember though that many athletes find no need for Nolvadex while others absolutely need it to avoid a gyno problem. One should be aware of how much they actually need an ancillary drug like this before committing to use it during a cycle. Should it be needed, Nolvadex is quite popular on the black market.