Topiramate (TPM) is an antiepileptic drug with a unique mode of action that is often useful in patients refractory to other drugs. However its use is restricted by the high incidence of cognitive adverse drug reactions (ADRs) that are associated with TPM exposure. TPM has been shown to cause particular cognitive ADRs, characterized by verbal fluency, attention, working memory and language deficits, at a much higher rate than other antiepileptic drugs. There do not appear to be obvious differences between patients that do or do not experience cognitive ADRs when on TPM (e.g. age, sex, concomitant medications, diagnosis), which suggests a genetic contributor.