A randomized, double-blind, placebo-controlled, multicenter study that assessed the endometrial effects of norethindrone acetate plus ethinyl estradiol versus ethinyl estradiol alone.

Objective: The purpose of this study was to determine the incidence of endometrial hyperplasia in subjects who receive continuous norethindrone acetate and ethinyl estradiol combinations versus unopposed ethinyl estradiol.

Study Design: Nine hundred forty-five postmenopausal women were randomly selected for 12 months of treatment with one of six blinded norethindrone acetate/ethinyl estradiol combinations (milligrams of norethindrone acetate/micrograms of ethinyl estradiol: 0/5, 0.25/5, 1/5, 0/10, 0.