CGRP is a 37 amino acid peptide synthesized in the central and peripheral nervous system from a calcitonin/CGRP gene complex. Two isoforms have been described which differ by three amino acids and display similar biological activities: CGRP-α, which is produced by alternative splicing of a calcitonin gene transcript, and CGRP-β, the product of a separate gene. In the CNS, CGRP acts as a neurotransmitter that is released from a subset of small sensory neurons that transmit pain information. In the circulation, CGRP is one of the most potent vasodilators known and may function as a regulator of blood flow. When administered systemically, CGRP causes hypotension in several species, including humans. Intradermal administration of CGRP at femtomole doses produces increased blood flow and persistent reddening.