Among women at high risk for breast cancer, fewer than one in five were inclined to take the drug tamoxifen to prevent the disease, according to a study by Joy Melnikow, professor of family and community medicine. Concerns about the drug's potential side effects were the primary reason. The study appeared in the May 15, 2005 issue of Cancer, a peer-reviewed journal of the American Cancer Society.

Taking tamoxifen can reduce a woman's risk of developing breast cancer by as much as 49 percent. However, the drug also increases risks for endometrial cancer, deep venous thrombosis, pulmonary embolism, painful sexual intercourse and cataracts requiring surgery.

"Potential harmful effects become much more important in the context of reducing risk for a potential disease, in contrast to treating a disease," Melnikow said. "To have successful risk-reducing agents for healthy people, it appears we will need agents with minimal side effects."