How the new drug works

Migraines are caused by a complex neurological condition which can trigger crippling headaches, nausea, blackouts, vomiting and even paralysis.

The new drug, erenumab, works in a completely different way, attacking the cause of migraines by stopping a protein which causes blood vessels in the brain to swell.

More than 8million Britons suffer from migraines, three-quarters of them women. Attacks last between four and 72 hours.

Sufferers experience an average of 13 attacks each year, usually in clusters or episodes of a few days. For about half a million, attacks come at least every other day.

Migraines are the sixth most common cause of disability around the world and are strongly linked to depression and absenteeism.

Current drugs include triptans, which deal with the symptoms but not the cause. If taken too often, they actually increase the frequency of attacks.