Packaging for a pre-filled pen for injecting the migraine drug fremanezumab, marketed as Ajovy. This is a preventative treatment that is injected once a month. It is a humanised 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. Fremanezumab was approved for treatment in the UK in 2020.