if left untreated, my migraines tend to last for 3 days -- and sometimes up to a week.
however, my doctor told me that preventatives are excellent for preventing migraines before they start. sometimes they don't eliminate your chances of getting a migraine, but they do cut down on them significantly.
my old neurologist who i used to see for my migraines once told me about rebound headaches. he said rebound headaches occur when a person takes too much tylenol. eventually, the body builds up a resistance to the tylenol and that causes rebound headaches.
right now i'm on a very low dose of topamax (25mg). my doctor said it will take 3-4 weeks before i'm able to tell a difference in my migraines. since this is such a low dose (the general rule with topamax is to always start patients off slow), she told me to expect that we will need to increase the topamax to a moderate or high dose. sometimes dosages for topamax can be as high as 100mg or 200mg, so if the 25mg doesn't work for me, we'll titrate up to 50mg, then 100mg and finally 200mg if needed.