Although oral contraceptives have been used by millions of women during the past 40 years, little is known about their long-term effects on health after their use is discontinued. Beral and colleagues have been monitoring the health of British women using oral contraceptives since 1968 and recently reported data from their study.
The study followed patients of 1,400 general practitioners in the United Kingdom. By monitoring health records and death certificates, the study covered 517,519 person-years of follow-up for women who had ever used oral contraceptives and 335,998 person-years for women who had never used them.
By 1993, the median age of study participants was 49 years, and the cohort had been followed for 25 years. During that time, 945 deaths occurred in the group of ever-users and 654 deaths occurred in the group of never-users. After adjustments for age, parity, social class and smoking, the relative risk of death for all causes was similar for users and nonusers of oral contraceptives.
For almost all causes of death, the relative risks of the two groups were similar. The exceptions were colorectal cancer and ovarian cancer, for which the relative risks of death were significantly reduced in ever-users, and cerebrovascular and violent or accidental deaths, for which the risks were significantly increased in ever-users. The risk of death within the first 10 years of oral contraceptive use was significantly increased for all causes, circulatory diseases and cerebrovascular disease but was significantly reduced for ovarian cancer. Women who used oral contraceptives for 10 years or more had excess mortality from lung and cervical cancer, but the excess deaths were related to smoking. No increase in mortality was found in women who had not used oral contraceptives for at least 10 years, including women reporting long durations of oral contraceptive use before discontinuation.
The authors conclude that the effects of oral contraceptive use on mortality are limited to current users and women who have used oral contraceptives within the previous 10 years. Although the women in this study predominantly used preparations with 50 mg of estrogen or more, no evidence was found of long-term increased mortality associated with prior oral contraceptive use. In particular, no evidence was found of a significantly increased risk of breast cancer or cancer of the reproductive tract in previous users of oral contraceptives.