The influence of oral contraceptives on the risk of multiple sclerosis.

To examine the risk of multiple sclerosis in users of combined oral contraceptives. Cohort study conducted between 1968 and 1996 using diagnostic data supplied by general practitioners General practices throughout the United Kingdom. Royal College of General Practitioners' Oral Contraception Study cohort of initially 46,000 women recruited during the late 1960s. Directly standardised incidence rates of multiple sclerosis were calculated for current, former and never-users of oral contraceptives using first ever cases of multiple sclerosis reported by the general practitioners. The standardisation variables were age, parity, social class and smoking history. Five-year survival rates in the different contraceptive groups were calculated using standard life table techniques. One hundred and fourteen first ever cases of multiple sclerosis had been reported by November 1996 during 564,000 woman-years of observation. The incidence rate in both current and former users was not materially different to that in never-users. Although based on limited evidence there was no suggestion that the five-year survival was affected by a woman's use of combined oral contraceptives. These findings do not suggest a greatly elevated risk of multiple sclerosis during, or after, use of combined oral contraceptives.