Rationale for a new triphasic oral contraceptive.

The association of progestogen and estrogen with certain undesirable effects led investigators to seek oral contraceptive (OC) formulations containing reduced amounts of both. Evidence is presented from studies of the triphasic regimen of 0.5 mg norethindrone plus 35 micrograms ethinyl estradiol on the first seven menstrual cycle days, 0.75 mg norethindrone plus 35 micrograms ethinyl estradiol the second seven days, followed by 1 mg norethindrone plus 35 micrograms ethinyl estradiol for the final seven days. This OC formulation appears to be highly effective and relatively free of the side effects commonly associated with low-dose OC regimens.