What is an Antiestrogen?

Antiestrogen is a substance that prevents cells from producing or utilizing estrogen, a female sex hormone. It is also known as estrogen blocker. Some scientists believe antiestrogen can reduce the growth of breast cancer cells, which may prevent or reduce the severity of breast cancer. Some bodybuilders also use antiestrogen products to increase muscle mass.

Antiestrogens are commonly divided into two groups: selective estrogen receptor modulators (SERMs) and aromatase inhibitors. SERMs promote antiestrogen effects in the body by manipulating the estrogen receptor, inhibiting estrogenic activity in some parts of the body. Aromatase inhibitors decrease the creation, or synthesis, of estrogen hormones.

SERMs are commonly used as an alternative to hormone replacement therapy (HRT), which uses estrogen to treat the symptoms of menopause, the permanent cessation of a woman's menstrual cycle. While HRT can increase the risk for breast cancer and blood clots, SERMs are seen as a safer alternative for women already at risk for these conditions. SERMs can also decrease the risk for osteoporosis, a common complication of menopause.

There are six types of SERMs currently used to treat menopause. Clomifene inhibits estrogenic activity in the hypothalamus, a portion of the brain located just above the brain stem. Femarelle, which is derived from soybeans, affects bone and brain tissue. Ormeloxifene, raloxifene, and tamoxifen affect the bone, uterus, and breast tissues. Toremifene is also used to inhibit estrogen production, although researchers have not indicated which tissues it targets to inhibit estrogenic activity.

Aromatase inhibitors are commonly used to treat breast cancer. Estrogen can cause cancerous breast cells to grow, but aromatase inhibitors prevent the production of this hormone. This can help prevent breast cancer from advancing and becoming more severe — and ultimately harder to treat. It is also used to prevent steroids from converting into estrogen, which can limit muscle growth in bodybuilders. It also may prevent testicular shrinkage and breast tissue growth in males, which commonly occur with steroid abuse.

Aromatase inhibitors are divided into two categories, called irreversible steroidal inhibitors and non-steroidal inhibitors. Irreversible steroidal inhibitors permanently bond to aromatase, which helps create estrogen hormones. Non-steroidal inhibitors do not bond to aromatase, but can still inhibit its ability to create estrogen. Non-steroidal inhibitors are used more than steroidal inhibitors.

Both types of antiestrogens reportedly reduce the risk for breast cancer and can ease the symptoms of menopause. Using antiestrogen supplements may cause some side effects, however. Acne, an increased sex drive, and facial hair growth are commonly reported side effects in both men and women. Women can also develop male-pattern baldness, hair growth on the chest and stomach, and changes in their menstrual cycles.