Epidemiologic studies of oral contraception.

Epidemiologic studies of oral contraception are of two main types: case-control and cohort. The best known cohort studies are the Royal College of General Practitioners' study and the Oxford-Family Planning Association study, both of which have been conducted in the United Kingdom. Combination oral contraceptives--both the older, higher-dose type, and the newer, lower-dose type--are highly effective if used properly. Noncontraceptive benefits of combination oral contraceptives include protective effects against menstrual disorders, anemia, benign breast disease, functional ovarian cysts, ovarian cancer, endometrial cancer, pelvic inflammatory disease, and uterine fibroids. Adverse effects include various cardiovascular problems, liver tumors, and the temporary impairment of fertility after stopping use, especially in older, nulliparous women. Effects, if any, on breast cancer and cervical cancer are still under evaluation. The often quoted cardiovascular risks of combination oral contraceptives are derived from studies of the older, higher-dose pills used in an outmoded way. There is evidence that modern pills, used by properly selected young women who are subsequently kept under surveillance, carry a minimal cardiovascular risk. A national study is currently in progress in the United Kingdom to try to confirm this.