[ashleynewman]

Based on what my doctors told me, migraines can be triggered by blood vessels constricting and dilating. Caffeine causes the same kind of motion, meaning it can cause migraines but also reverse them, which is why they are both a trigger and remedy.

[hilbert42]

That makes sense, ergotamine is a strong vascoconstrictor so that's why it works, it's constrictive effects would offset the dilative effects of the caffeine.