Hormonal contraception is not associated with increased risk for seizures in the general population: results from a cohort study using The Health Improvement Network.

Purpose: Endogenous human gonadal steroids and especially female sex hormones modulate the risk of developing epileptic seizures. In most circumstances, estrogens increase excitability, while progesterone bears substantial anticonvulsive properties. We questioned whether exogenous gonadal steroids used as hormonal contraception are associated with risk of seizures.

Methods: In a dynamic cohort ascertained within The Health Improvement Network database, we identified 2201 female patients aged 20-44 years with seizures during follow-up. In a nested case-control analysis, we matched these cases to 10,143 controls. Using logistic regression, we calculated the risk of seizure associated with use of contraceptives and adjusted for potential confounders. We performed same analyses among women with no prior hormonal contraception use ("new user" analyses) and in patients with a history of epilepsy.

Results: Unadjusted data suggested a lower risk for seizures in patients taking exogenous gonadal steroids irrespective of type of contraception used. After adjustment for potential confounders, neither use of combined oral contraceptives nor progestin-only oral contraceptives was associated with the risk for seizures overall. Analyses of "new users" of oral contraceptives produced similar risk estimates.

Conclusions: We found no evidence supporting an effect of oral exogenous gonadal steroids used for hormonal contraception on the risk of seizures in the general female population.