Smoking and cycle control among oral contraceptive users.

OBJECTIVE

Because cigarette smoking has a variety of antiestrogenic actions, we investigated the possibility that smoking may adversely affect spotting and bleeding among women using oral contraceptives.

STUDY DESIGN

Three open-label, randomized clinical trials involving 16,506 cycles among 2956 oral contraceptive users were performed.

RESULTS

Smokers reported a consistently higher frequency of spotting or bleeding than did nonsmokers. After recency and consistency of oral contraceptive use and progestin component were controlled for, smokers were, on average, 47% more likely to have spotting or bleeding than nonsmokers were over six cycles of oral contraceptive use, with higher levels of smoking associated with a greater frequency of spotting or bleeding. By the sixth cycle women who smoked > or = 16 cigarettes per day were almost three times more likely to have spotting or bleeding than were nonsmokers.

CONCLUSION

Cigarette smoking adversely affects cycle control among oral contraceptive users, possibly by increasing estrogen catabolism. Although these findings also raise the possibility that oral contraceptive efficacy may also be impaired in smokers, an immediate concern is that oral contraceptive users who have spotting and bleeding are more likely to discontinue their use, placing them at risk of unintended pregnancy.