A comparative study of three low dose progestogens, chlormadinone acetate, megestrol acetate and norethisterone, as oral contraceptives.

Three low dose progestogens, chlormadinone acetate (0-5 mg), megestrol acetate (0-5 mg) in oil, and norethisterone (0-35 mg), taken daily, were employed as oral contraceptives in postnatal women who desired to postpone their next pregnancy for up to a year. In a lower and middle social class population net pregnancy rates (life table) were five to six per 100 woman-years, of which about half were due to failure to take the tablets. Side effects other than menstrual disturbance were few. Norethisterone was the least likely of the three preparations to lead to discontinuation because of disturbance of menstruation. There were three ectopic gestations amongst 35 pregnancies in 4500 women-months of use. Ninety-five patients with varicose veins, 15 with a history of thrombophlebitis and 23 with a history of liver disease took progestogens without relevant untoward effects.