The safety of oral contraceptives: epidemiologic insights from the first 30 years

Abstract

Because oral contraceptives are used by tens of millions of healthy women, their safety for short-term and long-term use is an important issue that has been examined in a large number of epidemiologic studies. These studies have become more rigorous and have increased in size and analytic sophistication over the years. Although breast cancer remains the most important safety concern, the bulk of recent data suggests that oral contraceptives have no overall impact on a woman's risk of developing this disease. The results are less clear on the risk of cervical cancer and its precursors because of methodologic problems. However, the newer oral contraceptive formulations no longer appear to be associated with an increased risk of myocardial infarction or stroke.

PIP: Studies show that OCs have several benefits besides prevention of pregnancy. They protect against ovarian and endometrial cancer, pelvic inflammatory disease, and ectopic pregnancy. OCs also prevent iron deficiency anemia, primary dysmenorrhea, functional ovarian cysts, and benign breast disease. They may even protect against some benign uterine tumors, osteoporosis, toxic shock syndrome, and rheumatoid arthritis. Despite many concerns, some large studies have not identified an overall effect of OCs on breast cancer, but subgroup analyses showed increased risk in 30-34 year old women and in women with 1 child. A reanalysis of a large US study indicated an increase risk of breast cancer in nulliparous women with increasing use of OCs by young women. Cervical cancer is the leading cancer of women in developing countries which emphasizes the need to examine the link between OC use and cervical cancer. Several studies show an increased risk of cervical cancer. Several studies show an increased risk of cervical cancer in long term OC users. In 1 study, long term use meant 5 years. Yet these studies did not adequately address confounding factors such as smoking and sexual behavior. 3 case control studies in the US and the UK found an increased risk of liver cancer among OC users, yet a large case control study in developing countries did not find a link between OC use and liver cancer. Studies of high dose OCs found considerable increased risks of cardiovascular disease in OC users, but they did not take into account cigarette smoking which indeed increases the risk. Further health practitioners today do a more thorough job of identifying underlying medical problems before prescribing OCs. Moreover estrogen doses have fallen 10 fold since the original OCs. Finally, despite a transient delay, women who take OCs experience a return to fertility at the same rate as those who use other contraceptives.