Reduction in incidence of rheumatoid arthritis associated with oral contraceptives. Royal College of General Practitioners' Oral Contraception Study.

Analyses of the frequency of reporting of rheumatoid arthritis have been undertaken as part of the continuing major prospective survey of oral contraceptives. The rate of reporting in oral-contraceptive users (takers) is half of the rate in non-users (controls). The rates for ex-takers and controls are not materially different. The expected rise in the rate of reporting in women over 35 is apparent in controls but suppressed in takers. In the absence of any accountable bias, it is concluded that oral contraceptives protect against the development of rheumatoid arthritis. Although the effect is small, the observation may be valuable in understanding the aetiology of the disease and the mechanism of action of oral contraceptives.