Two regimens were selected, in addition to a placebo group. Women assigned to the intervention group who had previously undergone a hysterectomy were treated with unopposed estrogen, specifically conjugated estrogens (Premarin, manufactured by Wyeth), at a dosage of 0.625 mg/day ("E-alone," n = 5310; placebo, n = 5429). Women with an intact uterus were treated by a combined estrogen plus progestin regimen ("E+P," n = 8506; placebo, n = 8102), specifically the aforementioned estrogen regimen with the addition of 2.5 mg/day of medroxyprogesterone acetate (MPA; Prempro, also manufactured by Wyeth). The addition of progestin has been linked to a marked reduction in the risk for the development of endometrial cancer in women receiving estrogen treatment who have not undergone a hysterectomy.