Headaches were subjectively rated by participants as mild, moderate or severe. A headache day of at least moderate severity was defined as a calendar day (00:00 to 23:59) where the patient (using the electronic headache diary device) reports: - a day with headache pain that lasts ≥4 hours with a peak severity of at least moderate severity or - a day when the patient used acute migraine-specific medication (triptans or ergots) to treat a headache of any severity or duration. Monthly averages are derived and normalized to 28 days equivalent by the following formula: (# days of efficacy variable over relevant period / # days with assessments recorded in the e-diary over the relevant period) * 28. The change is calculated as post-baseline value - baseline value.

Full analysis set (FAS) included those in the intent to treat (ITT) population who received at least 1 dose of study drug and had at least 10 days of post-baseline efficacy assessments on the primary endpoint.

An adverse event (AE) was defined as any untoward medical occurrence that develops or worsens in severity during the conduct of a clinical study and does not necessarily have a causal relationship to the study drug. Severity was rated by the investigator on a scale of mild, moderate and severe, with severe= an AE which prevents usual activities. Relationship of AE to treatment was determined by the investigator. Serious AEs include death, a life-threatening adverse event, inpatient hospitalization or prolongation of existing hospitalization, persistent or significant disability or incapacity, a congenital anomaly or birth defect, OR an important medical event that jeopardized the patient and required medical intervention to prevent the previously listed serious outcomes.

Safety population

A migraine day was defined as when at least 1 of the following situations occurred: - a calendar day (0:00 to 23:59) demonstrating at least 4 consecutive hours of a headache endorsing criteria for migraine with or without aura - a calendar day (0:00 to 23:59) demonstrating at least 4 consecutive hours of a headache endorsing criteria for probable migraine, a migraine subtype where only 1 migraine criterion is missing - a calendar day (0:00 to 23:59) demonstrating a headache of any duration that was treated with migraine-specific medications (triptans and ergot compounds). Monthly averages are derived and normalized to 28 days equivalent by the following formula: (# days of efficacy variable over relevant period / # days with assessments recorded in the e-diary over the relevant period) * 28. The change is calculated as post-baseline value - baseline value.

Full analysis set (FAS)

Responder rates were defined as the percentage of total subjects who reached at least a 50% reduction in the monthly average of headache days (as subjectively reported by participants in the study diary) of at least moderate severity relative to the baseline period. For the overall analysis (Month 1-3), patients who discontinued early were considered non-responders. Monthly averages are derived and normalized to 28 days equivalent by the following formula: (# days of efficacy variable over relevant period / # days with assessments recorded in the e-diary over the relevant period) * 28. The percentage reduction in monthly average is calculated as: ((baseline value - post-baseline value) / baseline value) * 100.

FAS. One participant in the Placebo and Fremanezumab 675/225/225 mg treatment arms had 0 headache days of >= moderate severity during baseline and treatment and therefore was not included.

Participants recorded any migraine medications (name of drug, number of tablets/capsules, and the dose in milligrams per tablet/capsule) taken on each day in their electronic headache diary device. Acute migraine-specific medication included triptans or ergots. Monthly averages are derived and normalized to 28 days equivalent by the following formula: (# days of efficacy variable over relevant period / # days with assessments recorded in the e-diary over the relevant period) * 28. The change is calculated as post-baseline value - baseline value.

Full analysis set

Headaches were subjectively rated by participants as mild, moderate or severe. A headache day of at least moderate severity was defined as a calendar day (00:00 to 23:59) where the patient (using the electronic headache diary device) reports: - a day with headache pain that lasts ≥4 hours with a peak severity of at least moderate severity or - a day when the patient used acute migraine-specific medication (triptans or ergots) to treat a headache of any severity or duration. The change is calculated as post-baseline value - baseline value.

Full analysis set (FAS) included those in the ITT population who received at least 1 dose of study drug and had at least 10 days of post-baseline efficacy assessments on the primary endpoint.

A subset of patients (specified in the protocol not to exceed 30%) were allowed to use 1 concomitant migraine preventive medication. This outcome only includes those participants who did not take concomitant preventive migraine medication during this study. Headaches were subjectively rated by participants as mild, moderate or severe. A headache day of >= moderate severity was defined as a calendar day where the patient (using the electronic headache diary device) reports: - a day with headache pain that lasts ≥4 hours with a peak severity of >= moderate severity or - a day when the patient used acute migraine-specific medication (triptans or ergots) to treat a headache of any severity or duration. Monthly averages are derived and normalized to 28 days equivalent by the following formula: (# days of efficacy variable over relevant period / # days with assessments recorded in the e-diary over the relevant period) * 28. Change is post-baseline value - baseline value.

FAS of participants who did not receive concomitant preventive migraine medications.

The HIT-6 was developed by Kosinski et al (2003) as a short form for reliably assessing the adverse headache impact in clinical practice and clinical research settings. The questionnaire measures the adverse impact of headache on social functioning, role functioning, vitality, cognitive functioning, and psychological distress. It also assesses headache severity. Scores range from 36 to 78, where a higher score indicates a greater impact of headache on the daily life of the patient, i.e. scores ≤49 represent little or no impact, scores between 50 and 55 represent some impact, scores between 56 and 59 represent substantial impact; and scores ≥60 indicate severe impact. Negative change from baseline values indicate less adverse impact of headache.

Full analysis set

12-lead ECGs were performed before other assessments (eg, blood draws and administration of questionnaires) and performed in triplicate. The worst post-baseline finding for the participant is summarized. Only participants with both baseline and post-baseline ECGs are included. The ECG was evaluated by the investigator at the time of recording (signed and dated), and the printout was kept in the source documentation file. When potentially clinically significant findings were detected by the investigator, a cardiologist at a central diagnostic center was consulted for a definitive interpretation. Any ECG finding that was judged by the investigator as a potentially clinically significant change (worsening) compared with a baseline value was considered an adverse event. - NCS = abnormal, not clinically significant. - CS= abnormal, clinically significant. Shift format is: baseline finding / worst post-baseline finding.

Safety population of participants with both baseline and post-treatment ECGs.

Vital signs were performed before other assessments (eg, blood draws and administration of questionnaires). Vital signs with potentially clinically significant abnormal findings included: - Pulse Rate High: >=120 and increase of >=15 beats per minute - Pulse Rate Low: <=50 and decrease of >=15 beats per minute - Systolic Blood Pressure Low: <=90 mmHg and decrease of >=20 mmHg - Diastolic Blood Pressure High: >=105 mmHg and increase of >=15 mmHg - Diastolic Blood Pressure Low: <=50 mmHg and decrease of >=15 mmHg - Respiratory Rate Low: <10 breaths / minute

Safety population of participants with both baseline and post-treatment values for each vital sign.

Serum chemistry and hematology laboratory tests with potentially clinically significant abnormal findings included: - Blood Urea Nitrogen (BUN) High: >=10.71 mmol/L - Creatinine High: >=177 umol/L - Bilirubin High: >=34.2 umol/L - Alanine Aminotransferase (ALT): >=3*upper limit of normal (ULN) - Aspartate Aminotransferase (AST): >=3*upper limit of normal (ULN) - Gamma Glutamyl Transferase (GGT): >=3*upper limit of normal (ULN) - Hemoglobin: Male: <115 g/L or Female: <=95 g/L - Hematocrit: Male: <0.37 L/L or Female: <0.32 L/L - Leukocytes: >=20*10^9/L or <=3*10^9/L - Eosinophils/Leukocytes: >=10% - Platelets: >=700*10^9/L or <=75*10^9/L

Safety population of participants with at least one post-baseline result for the tests

Urinalysis with potentially clinically significant abnormal findings included: - Blood: >=2 unit increase from baseline - Urine Glucose (mg/dL): >=2 unit increase from baseline - Ketones (mg/dL): >=2 unit increase from baseline - Urine Protein (mg/dL): >=2 unit increase from baseline

Safety population of participants with at least one post-baseline result for the tests.

Shifts in prothrombin time from baseline to endpoint were summarized using patient counts grouped into three categories: - Low (below normal range) - Normal (within the normal range of 9.4 to 12.5 seconds) - High (above normal range) Shift format is: baseline finding / endpoint finding

Safety population of participants with both baseline and post-treatment values

Counts of participants who reported treatment-emergent injection site reactions as AEs are summarized. Preferred terms from MedDRA version 18.1 are offered without a threshold applied.

Safety population

The electronic Columbia-Suicide Severity Rating Scale (eC-SSRS) was used to assess the participant's suicidal ideation (severity and intensity) and behavior (Posner et al 2011). Suicidal behavior is defined as a "yes" answer to any of 5 suicidal behavior questions: preparatory acts or behavior, aborted attempt, interrupted attempt, actual attempt, and completed suicide. Suicidal ideation is defined as a "yes" answer to any one of 5 suicidal ideation questions: wish to be dead, and 4 different categories of active suicidal ideation.

The eC-SSRS Baseline/Screening version was completed by the participant at baseline, and the eC-SSRS Since Last Visit version was completed by the participant at all other time points. Any positive findings on the eC-SSRS Since Last Visit version required evaluation by a physician or doctoral-level psychologist. Findings after the first dose of study drug using the eC-SSRS Since Last Visit version are summarized.

Safety population