Estrogen blockers are most often used to treat breast cancer or to counteract the estrogenic effects of bodybuilding steroids. Estrogen blockers raise testosterone in men and increase strength and muscle mass. They also produce side effects that can range from fatigue to speech trouble.
There are three types of estrogen blockers: antiestrogens, aromatase inhibitors and specific estrogen receptor modulators. Common trade names of estrogen blockers include Clomid, Evista, Fareston and Soltamox.
Short term side effects of estrogen blockers include blurred vision, bruising, chest pain, dizziness, fatigue, headache, hot flashes, mood swings, night sweats, numbness, swelling and vaginal discharge.
Long term side effects of estrogen blockers include bone loss, blood clots, endometrial cancer, joint weakness, stroke and uterine cancer.
Antiestrogens such as Clomid may be used to treat infertility because they induce ovulation, but some women experience side effects, such as thickening of cervical mucus, that prevent conception.
A 2008 study at the University of London showed that women who experienced hot flashes while taking estrogen blockers for breast cancer were less likely to have a recurrence of the cancer.