How does propranolol prevent migraine headaches?

Propranolol belongs to a class of medication known as beta blockers which are most commonly used to treat high blood pressure and other heart problems. It is also commonly used to reduce the frequency and severity of migraine attacks. It is not known how it prevents migraines.

Research suggests that the use of propranolol decreases the frequency and severity of migraine headaches, but they have not yet completely understood the exact mechanism in propranolol that causes this effect. It is not yet known whether propranolol can treat a migraine after the onset of a migraine attack, so propranolol is usually prescribed to prevent migraine headaches, not to treat a migraine headache that has already started.