In 1991, the National Institutes of Health (N.I.H.) launched the Women’s Health Initiative (WHI), designed to test the effects of hormone therapy on heart disease, bone fractures, breast cancer and colon cancer. One group of women who had undergone a hysterectomy received oral estrogen (Premarin) alone [estrogen replacement therapy or ERT]. A second group received a combination of Premarin and progesterone (PremPro) [combination hormone replacement therapy or HRT]. A third group received a placebo, which contained no hormones. In 2002, the study was stopped because the Provera group was associated with a slight increase in the incidence of breast cancer, heart attack, stroke, and blood clots.