ORAL CONTRACEPTIVES AND VENOUS THROMBOEMBOLIC DISEASE, SURGICALLY CONFIRMED GALLBLADDER DISEASE, AND BREAST TUMOURS: Report from the Boston Collaborative Drug Surveillance Programme

Abstract

In a large hospital survey designed to identify associations between commonly used drugs and various diseases, three possibilities have been explored—namely, associations between oral-contraceptive use and "idiopathic" venous thromboembolism, surgically proven gallbladder disease, and breast tumours in women aged 20-44 years. Compared with non-users, the estimate of relative risk for thromboembolism in oral-contraceptive users was 11 (95% confidence limits; 5·2 and 25), and the estimated attack-rate attributable to oral contraceptives was 60 per 100,000 users per year. The corresponding relative risk for gallbladder disease was 2·0 (95% confidence limits: 1·4 and 2·9), and the estimated annual attack-rate was 79 per 100,000 users. In women below the age of 35 years, the frequency of gallbladder disease was significantly higher in those taking oral contraceptives for six to twelve months, compared with women who took them for longer periods. When breast cancer was studied, there was no evidence of a higher risk in oral-contraceptive users relative to non-users. A negative association between oral-contraceptive use and benign breast tumours was found, and this was more pronounced in women with fibroadenoma of the breast. Nearly all women in the survey took low-dose oestrogen preparations, and the role of dosage in relation to any of the above findings could not be evaluated.