Study of Oral Atogepant When Added to OnabotulinumtoxinA (BOTOX) to Assess Adverse Events and Change in Disease Activity in Adult Participants With Chronic Migraine

Inclusion Criteria:

• At least a 1-year history of chronic migraine (CM), with or without aura, consistentwith a diagnosis according to International Classification of Headache Disorders 3rdedition (ICHD-3 2018) and with or without acute medication overuse as defined in theprotocol.

• Must be currently treated with BOTOX for CM: treated with >= 2 treatment cycles inthe 8 months prior to Visit 2 (Day 1) with documentation of payer authorization orwritten attestation of self-pay to support continued use of BOTOX.

• Must have 8 to 23 (inclusive) migraine days in the electronic diary [eDiary]screening/baseline period (eDiary data must have been collected for at least 20days).

Exclusion Criteria:

• Use of opioid-containing products for more than 4 days per month for acute treatmentof headache in the 3 months prior to Screening or during the screening/baselineperiod.

• Treatment of study target muscles using acupuncture, transcutaneous electrical nervestimulation (TENS), cranial traction, dental splints for headache, or head and/orneck injections of anesthetics/steroids within 4 weeks prior to Screening andthroughout the study.

• Concurrent use of any migraine prevention treatment other than BOTOX (requiredconcomitant medication; or topiramate <=100mg daily) including use of oral gepantsin the 4 weeks prior to screening nor during the screening/baseline period.

• Current use or use within the 6 months (24 weeks) prior to Screening, of mAbsblocking the CGRP pathway.

• Concurrent use of oral gepants for acute migraine treatment in the 4 weeks prior toscreening nor during the screening/baseline period.