Been there, done that with practically every "preventative" Migraine medication out there. FYI - Imitrex and Frova are both "abortive medications", not preventatives.
Like I said, I've been through pretty much every preventative, in every catogory. Nothing ever worked for me. However, I am taking Cymbalta (90mg/day) for depression, but has the added bonus of helping chronic pain. It has not, however, stopped my migraines.
As for preventatives, let me highlight a few experiences I've had. I tried the blood pressure meds. I have a naturally low blood pressure, so meds like amitryptaline, were awful. Every time I moved quickly or stood up too fast...instant "room zooms". I was light-headed very frequently, and actually started to enjoy it, but it was not good for me.
I took Depakote for about eight months. It didn't help my migraines, but it did help me put on eightly pounds...bad news. Even worse, it gave me wicked dry mouth, which no one warned me about, and totally rotted all my teeth. I spent $4000 out of pocket, working with a dentist that turned out to be really lousy, then found a wonderful dentist who is redoing my whole mouth, which is now twice as bad, for a fraction of the cost. He has had to redo everything the last dentist did. AND, it made my migraines worse because the first dentist kept aggrevating my TMJ continuously for a year. TMJ is one of my worst migraine triggers.
I took Topamax for a while, but the side effects were stupendously bad, and which I've never fully recovered. Between my PCP, a pain specialist, and my Neurologist, I ended up on 400mg per day. I was practically comatose. I lost most of my mental function, had no short term memory, couldn't form sentances, lost my train of thought in the middle of a sentance, couldn't remember dates, couldn't remember words or used the wrong ones, etc...I was basically a mental midget, and I still have not completely recovered all my mental faculties. My short-term memory is still pretty fuzzy sometimes, and I quit the medication over two years ago.
I've still not found an adequate preventative, but I'm scheduled to see a Migraine Specialist at the University of Virginia Medical Center in March. I think in the meantime, I'm going to look into Migranol as an abortive, since I currently don't have anything to use.
Wish me luck. Hope this helps someone.