I've had Migraine for the last 20 years of my life, on and off, about monthly in the summer/winter and 4-8/month in the spring and fall. The frequency of the problem actually caused me to write a Visual Studio plug-in so I could use my monitor in low-contrast in a dark bedroom.
I didn't share the medication in the original post because there are a lot of caveats, but I take Depakote at 250mg twice daily and it works completely without side-effects (same dosage for 1.5 years and not a single instance of Migraine).
I happened upon this cure by accident, though, due to my body's intolerance for a myriad of common medicines used for Migraine treatment (and nothing OTC worked except Caffeine)
I cannot take Triptans (Maxalt/Imitrex). They work, but with huge mood side-effects. I was prescribed an anti-depressant (name escapes me) that showed promise in Migraine prevention. I got a Migraine headache while I was taking the anti-depressant and took a Maxalt (OKed by the doctor) and was hospitalized with Serotonin Syndrom. I cannot take anti-depressants, I learned later, due to my genetics[1].
I've seen many specialists but it wasn't until this hospital visit (on a holiday) followed by a misdiagnosis, that I was prescribed a rather high dose of Depakote (1000mg/day). It was prescribed in August and when I went through September without Migraine (this has never happened according to my log), I brought it to the attention of my headache specialist. He reduced the dosage at my request (Depakote is prescribed for BiPolar--an illness I do not have--and at the original dose, I felt emotionally flat[2]). At 500mg/day (2 doses), I don't have a single side-effect (other than headache relief, which is not why it is usually prescribed) and have been on that dose for 1.5 years without a single headache.
My headache specialist said that some of his other patients got relief from this medicine but that it's hit/miss. My experience is that this drug is basically everything you'd ever want in a treatment -- side-effect free, and works 100% of the time for me.
[1] Genesight test indicates that the medicine will remain in my system far longer than it should. I strongly recommend paying for this since it would have saved me a trip to the hospital. All of the SSRI medicines are in the high risk category for me. Glad I've never experienced depression!
[2] Nothing like the movies where a guy walks around with no expression on their face staring blankly. The best way I can describe it is that when something would happen and my wife would react, I'd feel like "Data from Star Trek" not understanding why she was reacting so strongly/emotionally. At this dose, I have the same level of intensity I'm used to.