In the Women’s Health Initiative study, 10,739 postmenopausal women 50 to 79 years of age who had undergone hysterectomy were randomized to receive 0.625 mg daily of conjugated equine estrogens (CEE; Premarin) or placebo. The participants were seen at 40 clinical centers in the United States starting in 1993 and continuing until the trial was ended after 6.8 years rather than after 8.5 years as planned. Follow up averaged 7.1 years. At the end of the study, 54% of women assigned to receive CEE and 53.5% of those assigned to placebo had stopped using their study medication.