Tamoxifen, an antiestrogen medicine commonly used for treating breast cancer, often causes hot flashes as a side effect. Hot flashes can be uncomfortable and disrupt a woman's normal activities, including sleep. Estrogen replacement hormones are used to treat hot flashes in women without breast cancer but cannot be used in breast cancer patients because they might cause the cancer to grow. Some studies have shown that clonidine, a nonhormonal medicine sometimes used to treat high blood pressure, can reduce hot flashes in women who have gone through natural menopause, but other studies have not shown that effect.