Onabotulinum toxin A (botulinum toxin type A, Botox®) is a focally acting neurotoxin that inhibits the release of neurotransmitters from presynaptic nerves. Preclinical evidence has shown that onabotulinum toxin A has anti-inflammation and antinociceptive properties. Onabotulinum toxin A is a safe and effective treatment for chronic migraine. Seven botulinum toxin serotypes are produced by Clostridium botulinum (i.e., A, B, C, D, E, F, and G). Botulinum toxins consist of a heavy chain of 100 kDa and a light chain of 50 kDa linked by a single disulfide bond and are synthesized as a relatively inactive single-chain polypeptide.