Do oral contraceptives reduce the incidence of rheumatoid arthritis? A pilot study using the Stockholm County medical information system.

The Stockholm County medical information system was used to select cases for a pilot study on the association between oral contraceptive (OC) use and the incidence of rheumatoid arthritis (RA). A selection procedure is described by which we obtained 76 cases of RA. These were compared in a case-control study with 152 healthy controls with regard to OC use prior to the onset of RA. For all women who had used OCs for more than one year the relative risk of RA was 0.70 (0.40, 1.24). The relative risk decreased with advancing age at onset of RA, being 0.40 (0.10, 1.65) for women with age at onset over 40. Although the material is small, and there are some inconsistencies in the results, our findings are compatible with the hypothesis that the use of OCs is associated with a reduced incidence of RA.