While estrogen is often a hormone more associated with women, there are several reasons why tamoxifen, a drug used to block the effects of estrogen, may be used to treat men. Men who get breast cancer are often treated with a course of tamoxifen. It can also be useful to stop or reverse a condition called gynecomastia, where the breast tissue of adolescent boys or men grows and sometimes becomes uncomfortable. Another use is tamoxifen for men who take anabolic steroids, in order to block the large amounts of estrogen produced by their bodies once they stop taking them.
One of the primary uses of tamoxifen for men is the treatment of breast cancer. While this type of cancer is fairly rare in men, the type that most men get involves tumors that are estrogen receptor-positive, meaning that estrogen encourages their growth. Since tamoxifen is a selective estrogen receptor modulator, or SERM, it helps to keep estrogen from binding to the proteins on these tumors and therefore inhibits their growth. It can be used in situations where the cancer is in early stages, and also when it has progressed and metastatized to other parts of the body.
Doctors also use tamoxifen for men who suffer from gynecomastia, where the breasts become enlarged and often sore or tender. This condition can occur in boys during puberty or in grown men, and may be the result of a number of causes, including normal pubertal hormone shifts, taking certain medications, or treatment for other conditions like prostate cancer and HIV/AIDS. The cause may also simply be unknown. Though gynecomastia can resolve on its own in adolescent boys or may go away when medical issues resolve or drugs are discontinued, it may require treatment if it persists for an extensive period of time or becomes too uncomfortable or embarrassing for the patient. This is where a course of tamoxifen can be helpful, though it should be taken fairly soon after gynecomastia sets in, as it is typically not helpful when the condition has been present for a year or more.
One other possible use of tamoxifen for men is stopping certain negative effects of anabolic steroids. Bodybuilders and other athletes who take steroids to improve performance suppress their production of the hormone androgen, and their bodies may compensate by overproducing estrogen. This can lead to gynecomastia and other negative effects, which tamoxifen can help block.