There have been at least 8 studies involving migraineurs and Magnesium which show that people who get migraines have low brain magnesium. However, finding your brain magnesium level is impractical. It seems that the best results for magnesium are for perimenstrual migraine prevention and as an acute abortive for migraine with aura. When it is used as an acute abortive, it is used as an IV infusion.
One problem the studies found is that the oral formulations for magnesium differ in the different studies. In addition, those with low levels of magnesium seem to respond better overall as opposed to those with normal blood levels of magnesium but who may have low magnesium in their cells (which can’t be tested).
There are some doctors who recommend a high dose of magnesium such as 600mg a day to be of benefit. Dr. Mauskop of the NY Headache Center, one of these researchers, feels that a daily dose of a chelated or slow-release oral magnesium used for at least 4 months is helpful.
Some other physicians such as Dr. Stephen Silberstein on the Jefferson Headache Center feels that magnesium at doses of 600mg a day are most helpful for migraines in pregnant women and as an additional medication to other medications when given IV to get rid of a bad headache.
The main side effect is diarrhea and some stomach upset which is caused by poorly absorbed magnesium. There are some Magnesium formulations that do not cause diarrhea and also help with constipation and improved sleep.