1. Number of Participants With Adverse Events (AEs) [Up to approximately 28 Weeks]
   An adverse event (AE) is defined as any untoward medical occurrence in a patient or clinical investigation participant administered a pharmaceutical product which does not necessarily have a causal relationship with this treatment. The investigator assesses the relationship of each event to the use of study. A serious adverse event (SAE) is an event that results in death, is life-threatening, requires or prolongs hospitalization, results in a congenital anomaly, persistent or significant disability/incapacity or is an important medical event that, based on medical judgment, may jeopardize the participant and may require medical or surgical intervention to prevent any of the outcomes listed above.
2. Responder Status of at least 25% Reduction in the Frequency of Monthly Migraine Days Collected via Daily Electronic Diary (eDiary) [Baseline (Week 0) through 24 Weeks]
   Percentage of participants achieving at least 25% reduction from baseline in the frequency of monthly migraine days will be assessed.
3. Responder Status of at least 30% Reduction in the Frequency of Monthly Migraine Days Collected via eDiary [Baseline (Week 0) through 24 Weeks]
   Percentage of participants achieving at least 30% reduction from baseline in the frequency of monthly migraine days will be assessed.
4. Responder Status of at least 50% Reduction in the Frequency of Monthly Migraine Days Collected via eDiary [Baseline (Week 0) through 24 Weeks]
   Percentage of participants achieving at least 50% reduction from baseline in the frequency of monthly migraine days will be assessed.
5. Responder Status of at least 75% Reduction in the Frequency of Monthly Migraine Days Collected via eDiary [Baseline (Week 0) through 24 Weeks]
   Percentage of participants achieving at least 75% reduction from baseline in the frequency of monthly migraine days will be assessed.
6. Responder Status of at least 100% Reduction in the Frequency of Monthly Migraine Days Collected via eDiary [Baseline (Week 0) through 24 Weeks]
   Percentage of participants achieving at least 100% reduction from baseline in the frequency of monthly migraine days will be assessed.
7. Change From Baseline in Monthly Migraine Days [Baseline (Week 0) through 24 Weeks]
   Change from Baseline in monthly migraine days, defined by International Headache Society (IHS) Guidelines 2018 will be assessed.
8. Change from Baseline in Monthly Headache Days, Moderate or Severe Headache Days, Cumulative Hours of Headache, Acute Treatment Medication Use Days, Headache Free Days, and Migraine Symptom-Free Days [Baseline (Week 0) through 24 Weeks]
   Change from baseline in monthly headache days, moderate or severe headache days, cumulative hours of headache, acute treatment medication use days, headache free days, and migraine symptom-free days, defined by IHS Guidelines 2018 will be assessed.
9. Change from Baseline in Monthly days with Non-Headache Migraine Symptoms [Baseline (Week 0) through 24 Weeks]
   Change from baseline in monthly days with non-headache migraine symptoms such as photophobia, phonophobia, nausea and/or vomiting, dizziness, neck pain, tiredness, mood change, yawning, thirst, cravings, urinary frequency, cranial autonomic symptoms
10. Change from Baseline in Monthly Activity Impairment in Migraine - Diary (AIM-D) [Baseline (Week 0) through 24 Weeks]
    The AIM-D is an 11-item daily diary measure that assesses the impact of migraine and is comprised of two domains that evaluate performance of daily activities (7 items) and physical impairment (4 items).

• Chronic Migraine

Drug: Atogepant

Oral Tablet

Experimental: Atogepant
Participants will receive atogepant once a day (QD) during the 24-week treatment period.

• Drug: Atogepant

Inclusion Criteria:

• At least a 1-year history of chronic migraine (CM), with or without aura, consistent with a diagnosis according to International Classification of Headache Disorders 3rd edition (ICHD-3 2018) and with or without acute medication overuse as defined in the protocol.
• Must be currently treated with BOTOX for CM: treated with >= 2 treatment cycles in the 8 months prior to Visit 2 (Day 1) with documentation of payer authorization or written 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 20 days).

Exclusion Criteria:

• Use of opioid-containing products for more than 4 days per month for acute treatment of headache in the 3 months prior to Screening or during the screening/baseline period.
• Treatment of study target muscles using acupuncture, transcutaneous electrical nerve stimulation (TENS), cranial traction, dental splints for headache, or head and/or neck injections of anesthetics/steroids within 4 weeks prior to Screening and throughout the study.
• Concurrent use of any migraine prevention treatment other than BOTOX (required concomitant medication; or topiramate <=100mg daily) including use of oral gepants in 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 mAbs blocking the CGRP pathway.
• Concurrent use of oral gepants for acute migraine treatment in the 4 weeks prior to screening nor during the screening/baseline period.

Studies a U.S. FDA-regulated Drug Product: Yes

Studies a U.S. FDA-regulated Device Product: No

Product Manufactured in and Exported from the U.S.: No