Risk of myocardial infarction in relation to current and discontinued use of oral contraceptives.

In a hospital-based case-control study, we evaluated the rate of myocardial infarction in relation to discontinued as well as current use of oral contraceptives. We compared 556 women with infarction, 25 to 49 years old, with 2036 age-matched control subjects. For current users, the rate-ratio estimate was 3.5 (95 per cent confidence limits, 2.2 to 5.5). For past users 40 to 49 years of age, the magnitude of the rate ratio was related to the duration of use: for total durations of past use of less than five years, five to nine years, and 10 or more years, respectively, the rate-ratio estimates (with 95 per cent confidence limits) were 1.0 (0.8 and 1.4), 1.6 (1.1 and 2.5), and 2.5 (1.5 and 4.1). This trend was statistically significant (P less than 0.01). The findings suggest that an effect on the risk of myocardial infarction persists after the discontinuation of long-term use of oral contraceptives.