Study rates real-world effectiveness of oral contraceptives

February 1, 2011

The 24-day oral contraceptive regimens containing a progestogen with a long half-life are generally more effective than conventional 21-day regimens.

The 24-day oral contraceptive (OC) regimens containing a progestogen with a long half-life are generally more effective than conventional 21-day regimens, according to the findings of a recent large, prospective trial.

Although all OCs boast failure rates well below 1% if used correctly and consistently, they frequently are not used properly. The longer-acting ingredients in the 24-day oral formula (coverage lasts about 30 hours) combined with the shorter break between days of taking the active pills helps to provide coverage for forgotten pills; that is, they better suppress progestogen levels even during the pill-free interval.

Researchers looked at outcome data from 52,218 US participants in the International Active Surveillance of Women Taking Oral Contraceptives study, a controlled, noninterventional, long-term, cohort study with active surveillance of the study participants. Over the course of the study, more than 1,600 women became pregnant unintentionally. About 1,400 of these were due to imperfect use of their OC, ascribed to forgetting to take the pill on time (46.3%), taking antibiotics (21.1%), or experiencing diarrhea or vomiting (9.5%). Researchers calculated the failure rates of the 24-day regimen of drospirenone and ethinyl estradiol and the 21-day regimens of other progestogens to be 2.1% and 3.5%, respectively, after the first study year and 4.7% and 6.7%, respectively, after the third year. The adjusted hazard ratio was 0.7 (95% CI, 0.6–0.8). Direct comparisons of the 24-day and 21-day regimens of drospirenone and norethisterone, respectively, revealed lower contraceptive failure rates with the 24-day regimens.

Dinger J, Minh TD, Buttmann N, Bardenheuer K. Effectiveness of oral contraceptive pills in a large US cohort comparing progestogen and regimen. Obstet Gynecol. 2011;117(1):33-40.