Background: Oral contraceptives induce hypertension in approximately 5% of users of high-dose pills that contain at least 50 micrograms estrogen and 1 to 4 mg progestin, and small increases in blood pressure have been reported even among users of modern low-dose formulations. However, neither the responsible hormone in the oral contraceptive nor particular subgroups of women who might be susceptible to the hypertensive effect of oral contraceptives have been identified.
Methods and results: In a prospective cohort study in the United States, 68 297 female nurses aged 25 to 42 years and free of diagnosed hypertension, diabetes, coronary heart disease, stroke, and cancer at baseline were followed up for 4 years. During 231 006 person-years of follow-up, 1567 incident cases of hypertension were diagnosed. Compared with women who had never used oral contraceptives, the age-adjusted relative risk was 1.5 (95% CI = 1.2 to 1.8) for current use and 1.1 (95% CI = 0.9 to 1.2) for past use. After adjustment for age, body mass index, hormones cigarette smoking, family history of hypertension, parity, physical activity, alcohol intake, and ethnicity, current users of oral contraceptives had an increased risk of development of hypertension (RR = 1.8; 95% CI = 1.5 to 2.3) compared with women who had never used them. The multivariate relative risk for past users was 1.2 (95% CI = 1.0 to 1.4). There were no important modifying effects of age, family history of hypertension, ethnicity, or body mass index.
Conclusions: Current users of oral contraceptives had a significant, moderately increased risk of hypertension. However, among this group, only 41.5 cases per 10 000 person-years could be attributed to oral contraceptive use. Risk decreased quickly with cessation of oral contraceptives, and past users appeared to have only a slightly increased risk.