Packaging for an auto-injector device of the migraine drug Erenumab, sold under the brand name Aimovig. This is a preventative treatment that is injected once a month. It is a monoclonal antibody that blocks the calcitonin gene-related peptide receptor (CGRPR). Calcitonin gene-related peptide (CGRP) is a small protein that is released as a result of brain changes during migraine. Binding of CGRP to its receptor causes vasodilation (the widening of blood vessels) in the brain, which leads to headache. Erenumab was the first CGRPR antagonist to be approved for treatment of migraine.