Optimum dosage of an oral contraceptive. A report from the study of seven combinations of norgestimate and ethinyl estradiol.

A statistically designed study was carried out to determine an optimum combination of norgestimate and ethinyl estradiol as an oral contraceptive, based on efficacy, safety, and side-effect patterns. A total of 1,991 patients were studied for more than two years while they were receiving various dosage combinations of these steroids. There were seven dosage combinations studied as part of a statistically orthogonal experimental design, augmented by three combinations near the center. The data arising from these studies were used to fit approximate functions relating the amount of norgestimate and ethinyl estradiol to the rate of spotting and breakthrough bleeding, gastrointestinal disturbance, and pregnancies. These functions, in turn, helped to identify an optimum dosage (0.125 mg. of norgestimate plus 0.035 mg. of ethinyl estradiol) in the entire range of combinations studied.