Oral contraceptives and rheumatoid arthritis: further evidence for a preventive effect.

To investigate a reported negative association between the use of oral contraceptives (OC) and the development of rheumatoid arthritis, a case-control study was undertaken to compare the histories of OC use between 228 women with a diagnosis of probable or definite rheumatoid arthritis and 302 women with the diagnosis of soft-tissue rheumatism and/or osteoarthritis. The use of OCs before the onset of joint complaints was acknowledged by 31.1% of the rheumatoid arthritis patients and by 55.6% of the controls. After adjustment for possible confounding variables, the rate ratio for ever use became 0.42 (95% confidence interval 0.27--0.65), while it was 0.40 (0.22-0.72) for ex-users and 0.45 (0.28-0.75) for current users. These findings confirm the finding from the Royal College of General Practitioners Oral Contraceptive Study that the incidence rate of rheumatoid arthritis among OC users was halved.