A Study to Evaluate the Effectiveness and Safety of Dysport® for the Prevention of Chronic Migraine in Adults

Inclusion Criteria :

• Participant must be ≥18 years of age inclusive, at the time of signing the informed consent and privacy/data protection documentation

• Participant has a diagnosis for more than 12 months, prior to screening visit, of chronic migraine according to the International Classification of Headache Disorders definition and diagnostic criteria

• Migraine onset occurred when participant was <50 years of age

• Has baseline number of monthly headache days (MHD) ≥15 and baseline number of monthly migraine days (MMD) of ≥8, using eDiary data collected during the 4 weeks nearest to randomisation on Day 1 (but prior to randomisation)

• Has baseline number of valid diary days ≥22 days collected during the 4 weeks nearest to randomisation on Day 1

• Participant must have previously used, or is currently using, preventive treatment for migraine (pharmacological) (i.e. non-naïve) prior to start of screening eDiary

Exclusion Criteria :

• History or current diagnosis of migraine with brainstem aura, retinal migraine, complications of migraine, tension-type headache, trigeminal autonomic cephalalgias, hypnic headache, hemicrania continua, or new daily persistent headache

• Headache attributed to another disorder (e.g. secondary headaches), except medication overuse headache, which is permitted

• Use of any of the following medications in the specified timeframe prior to start of the screening daily headache eDiary:

1. Within 24 weeks

• i. Botulinum toxin for migraine (or for any other medical/aesthetic reason within 16 weeks)

2. Within 12 weeks

• i. CGRP antagonists (monoclonal antibody or gepant) for preventive treatment of migraine (acute treatment of headache/migraine with a gepant is permitted but limited to no more than 6 days per month (i.e 6 days per each 4-week period with gepant intake))

• ii. Cannabidiol or other types of cannabinoids

3. Within 4 weeks

• i. Anaesthetic or steroid injection in any region targeted for injection with study intervention

• ii. Use of medical device to treat migraine (e.g. non-invasive neuromodulation therapies such as nerve stimulation (gammaCore), transcranial magnetic stimulation (cephaly), external trigeminal nerve stimulation, transcutaneous electrical nerve stimulation, and peripheral neuroelectrical stimulation)

• iii. Other interventions for migraine assessed to interfere with study evaluations (e.g. acupuncture in head and neck region, cranial traction, nociceptive trigeminal inhibition, occipital nerve block treatments, and dental splints for headache) iv. Use of opioids or barbiturates for more than 2 days/month. Note: participants are permitted to take one concomitant migraine preventative treatment (not listed above); however, the dose of this medication should be stable for ≥3 months before start of the screening eDiary

• Known history of treatment failure to more than four medications prescribed for the prevention of migraine (two of which have different mechanisms of action) or known history of treatment failure to botulinum toxin prescribed for the prevention of migraine.