Botox (onabotulinum toxin A) was licensed specifically for the treatment of chronic migraine in July 2010 by the Medicines and Healthcare products Regulatory Agency (MHRA).
The NICE guidelines can be viewed and downloaded at https://www.nice.org.uk/guidance/ta260/resources/botulinum-toxin-typea-for-the-prevention-of-headaches-in-adults-with-chronic-migraine-pdf-82600545273541
