Migraine Pathology:

A migraine is characterized by variables that may include nausea, vomiting, visual scotomas.  It is followed by a severe throbbing headache that lasts between 1 and 2 hours.  Trigeminal nerve distributes to the intracranial arteries where they release calcitonin gene-related peptide (CGRP), a potent vasodilator.  Vasodilation of the intracranial arteries causes a migraine.

Migraine treatment:

Triptans : They are partial 5-HT1D/B agonists, they increase intracranial vasoconstriction that counteracts vasodilation that causes pain in migraine.

Ergot alkaloids : They are mixed partial agonists at 5-HT2 and alpha receptors, they cause vasoconstriction.

Beta-blockers : (Clonidine)  It is a agonist at alpha2 receptors in the CNS.  It reduces sympathetic tone and increases parasympathetic tone resulting in vasoconstriction.

Calcitonin gene-related peptide(CGRP) blockers : (Telgepant, Olcegepant) They block the vasodilatory action of CGRP.