The dose of Topamax is slowly titrated up to reach the therapeutic dose levels. This is done to improve
patient response and improve tolerability.So in a way you can say that it takes time to enter the system.
Some of the common side effects of topiramate that are seen when it is used as a preventive therapy for migraine are tiredness, mood swings, anxiety, insomnia, depression, pins and needles sensation and difficulty with language.
http://en.wikipedia.