Epidemiology of the noncontraceptive effects of oral contraceptives.

Epidemiologic studies have made major contributions to our understanding of oral contraceptive safety. The findings of major studies of the risk of cardiovascular disease and neoplasia associated with oral contraceptive use are reviewed, with discussion of the many factors to be considered in the interpretation of conflicting results. Mortality data that were based on earlier oral contraceptive formulations, dosage, and usage patterns may not be relevant to current practices. Recent studies suggest that reduced doses of estrogens and progestins in current oral contraceptive formulations and better screening of patients have reduced the risks of cardiovascular disease associated with oral contraceptive use, with the most important exception being an increased risk among older women who smoke. While most epidemiologic studies demonstrate no overall association between oral contraceptives and breast cancer, unanswered questions remain concerning this relationship.