If Topiramate is taking for epilepsy, it can take a couple of weeks to work however will reach full effectiveness after 6-8 weeks. If taken for migraines, normally people experience a reduction in migraine occurrence after a month. However, it may take up to 3 months to notice the full benefits of the drug. However, it works differently for everyone. Topiramate stays in your system for 4-6 days following the last time you had your dose.