By the way, doctor: How can caffeine help migraines?
Q. If coffee constricts blood vessels, why would it help migraine sufferers, since the constriction curtails blood flow, which would seem to cause more pain?
A. The simple notion that migraines are caused by the expansion of blood vessels (vasodilation) on the surface of the brain is, well, too simple. Migraines are complicated. Abnormal brain activity may precede vasodilation, but I think vasodilation is probably responsible for the painful part of the migraine attack. Caffeine tends to constrict blood vessels, which would seem to cause pain by cutting off blood flow. But mid-migraine, caffeine may relieve pain by returning enlarged and painfully distorted arteries back to their pain-free state.
Perhaps there's another explanation for caffeine's effect, but it's clear from experience that caffeine, especially in the form of coffee, helps many people with migraines. But there are individual differences — in migraine and in the response to caffeine. For some, caffeine triggers migraines.