Oral contraception and stroke. Evidence from the Royal College of General Practitioners' Oral Contraception Study.

Abstract

A nested case-control analysis of data collected during the prospective Royal College of General Practitioners' Oral Contraception Study was performed to examine the relation between use of oral contraception and risk of stroke. The 253 women who had a first-ever stroke (International Classification of Diseases, eighth revision, codes 4300 to 4389) or amaurosis fugax (code 3791) between 1968 and 1990 (case subjects) were compared with 759 women who did not have this diagnosis (control subjects). Smoking, social class, and history of hypertension were found to be important risk factors for stroke. Women who had ever used oral contraceptives had an increased risk of all stroke (odds ratio, 1.5; 95% confidence interval, 1.1 to 2.0, adjusted for smoking and social class) and of a fatal event (adjusted odds ratio, 2.3; 95% confidence interval, 1.2 to 4.4). A significant doubling of all stroke risk was observed among current users, an effect that was apparent in both smokers and nonsmokers. Former users had a small nonsignificant elevation in risk of all stroke but a stronger risk of a fatal event. The effects in former users appeared to be restricted to women who smoked. Current users of oral contraceptives appeared to be at increased risk of stroke. There is some evidence that former users may also have a persisting effect, although further research is needed to confirm these observations.