The ZAN-BPD is a clinician-administered scale designed to assess severity of disease symptoms in participants with BPD based on clinician rating on 9 criteria. Each of the 9 criteria for BPD was rated on a 5-point anchored rating scale of 0 to 4. These scores were clustered into 4 sector scores (akin to domains) and a total score. The 4 sector scores added up to provide the overall total score for the ZAN-BPD, which ranged from 0 to 36. A higher score represented a higher severity of disease symptoms. Mixed model repeated measures = MMRM, antidepressant therapy = ADT.

FAS for enriched participants is a subset of randomized population who met pre-defined criteria and who received at least 1 dose of double-blind investigational medicinal product (IMP) and had a baseline value and at least 1 valid post-randomization efficacy evaluation for ZAN-BPD total score. Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure.

The severity of illness for each participant was rated using the CGI-S. CGI-S is an observer-rated scale with a total score range of 0 to 7 where a higher score represented a worse outcome. The response choices were 0 = not assessed; 1 = normal, not at all ill; 2 = borderline ill; 3 = mildly ill; 4 = moderately ill; 5 = markedly ill; 6 = severely ill; and 7 = among the most extremely ill participants.

FAS for enriched participants is a subset of randomized population who met pre-defined criteria and who received at least 1 valid post-randomization efficacy evaluation for ZAN-BPD total score. Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure.

PGI-S is a 7-point single-item self-report scale for the participant to rate the severity of symptoms of BPD ranging from 0 to 7 where 1 denoted no symptoms and 7 denoted very severe.

FAS for enriched participants is a subset of randomized population who met pre-defined criteria and who received at least 1 valid post-randomization efficacy evaluation for ZAN-BPD total score. Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

A 7-point single-item self-report scale depicting a participant's rating of overall change in their condition since starting trial medication. Participants answered the question: "Since starting study medication, how much have their symptoms of Borderline Personality Disorder changed?" with a score ranging from 1 to 7 where 1 denoted very much improved and 7 denoted very much worse.

FAS for enriched participants is a subset of randomized population who met pre-defined criteria and who received at least 1 valid post-randomization efficacy evaluation for ZAN-BPD total score. Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

Participant's condition was assessed using CGI-I scale. CGI-I is an observer-rated scale with a total score of 0 to 7 and a higher score represents a worse outcome. The score included the following response choices: 0 = not assessed; 1 = normal, not at all ill; 2 = borderline ill; 3 = mildly ill; 4 = moderately ill; 5 = markedly ill; 6 = severely ill; and 7 = among the most extremely ill participants.

FAS for enriched participants is a subset of randomized population who met pre-defined criteria and who received at least 1 valid post-randomization efficacy evaluation for ZAN-BPD total score. Number analyzed = number of participants with data available for analyses at the specified time point.

An adverse event (AE) is any untoward medical occurrence in a clinical trial participant administered an IMP and which does not necessarily have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease temporally associated with the use of a medicinal (investigational) product, whether or not related to the medicinal (investigational) product. A TEAE is defined as an AE that started after start of study treatment.

Safety population (SP) included those participants who received at least 1 dose of study drug (brexpiprazole or placebo).

Laboratory parameters included hematology(Hem), serum chemistry(Che) and urinalysis(Uri). Criterion:Che-Alkaline Phosphatase (Units/liter [U/L]):≥3 x ULN, Aspartate Aminotransferase (U/L):≥3 x ULN,Bilirubin (mg/deciliter[dL]):≥2.0,Cholesterol(Cho);Cho,fasting(mg/dl):≥240,Creatine Kinase(U/L):≥3 x ULN, Creatinine(mg/dL):≥2.0,Glucose (Glu);Glu,fasting(mg/dL):100,High Density Lipoprotein (HDL) Cho (mg/dL):Male (M) < 40or Female (F) <50, Low Density Lipoprotein (LDL) Cho(mg/dL):≥160,Prolactin (nanograms/milliliter [ng/mL]):>1 x ULN,Triglyceride (mg/dL):≥150,Urate(mg/dL): M ≥10.5 or F ≥8.5,Urea Nitrogen (mg/dL):≥30,Hem-Eosinophils (Eosi) (10^9 L):≥10%,Hematocrit (%): M ≤37% and ≥3 percentage (per) point decrease from baseline or F≤32% and ≥3per point decrease from baseline, Hemaglobin(gram per deciliter [g/dL]):M ≤11.5 or F ≤9.5,Leukocytes(10^9/L):≤2.8 x10^3/uL,≤16.0 x10^3/uL,Platelets(10^9/L):≤75 x10^3/ uL,≥700 x10^3/uL,Uri-Glu,urine; Protein,urine:Increase of ≥2U.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Only those categories with at least one participant with event are reported. Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = total number of participants with at least one post-baseline numeric result for given laboratory parameter.

New onset (> 1 x upper limit of normal {ULN}, > 2 x ULN, 3 X ULN) prolactin means a participant who attains a categorical change during treatment phase but not at baseline. Only those categories with at least one participant with event are reported.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure.

Vital Signs included orthostatic hypotension, heart rate (HR), systolic and diastolic blood pressure (bp), and weight. Potential clinical relevance criterion: Orthostatic Hypotension:>= 20 millimeters of mercury (mmhg) decrease in systolic bp and >= 25 beats per minute (bpm) increase in HR from supine to standing; HR Standing (bpm):< 50 and decrease >= 15,> 120 and increase >= 15; HR Supine (bpm): < 50 and decrease >= 15,>120 and increase >= 15; Systolic BP Standing (mmhg):< 90 and decrease >=20,> 180 and increase >= 20; Systolic BP Supine (mmhg):< 90 and decrease >= 20, >180 and increase >= 20; Diastolic BP Standing (mmHg): < 50 and decrease >= 15,> 105 and increase >= 15; Diastolic BP Supine (mmHg):< 50 and decrease >= 15, > 105 and increase >= 15; Weight (kilograms[kg]): Decrease or increase >= 7%. Only those categories with at least one participant with event are reported.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analyses for this outcome measure.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analyses for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed= number of participants with data available for analyses for this outcome measure. Number analyzed= number of participants with data available for analyses at the specified time point.

BMI is defined as weight in kilograms divided by the square of height in meters.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed= number of participants with data available for analyses for this outcome measure. Number analyzed= number of participants with data available for analyses at the specified time point.

ECG parameters analyzed included rhythm, conduction and ST/T morphology. Potential clinical relevance criterion: Rhythm- Supraventricular Premature Beat: not present at baseline and present post baseline, Ventricular Premature Beat: not present at baseline and present post baseline, Conduction- Right Bundle Branch Block: not present at baseline and present post baseline, ST/T Morphology- Symmetrical (Sym) T-Wave Inversion: not present at baseline and present post baseline. Only those categories with at least one participant with event are reported.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed= number of participants with data available for analyses for this outcome measure. Number analyzed = total number of participants with at least one post-baseline numeric result for the given ECG parameter.

The SAS consisted of a list of 10 symptoms of Parkinsonism (gait, arm dropping, shoulder shaking, elbow rigidity, wrist rigidity, head rotation, glabella tap, tremor, salivation, and akathisia). Each item was rated on a 5-point scale, with a score of zero representing the absence of symptoms and a score of 4 representing a severe condition. The SAS total score was the sum of the scores for all 10 items and ranged from 0 to 40. Higher scores indicated worst outcome.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

AIMS assessment consisted of 10 items describing symptoms of dyskinesia (muscles of facial expression, lips and perioral area, jaw, tongue, upper extremities, lower extremities, neck/shoulders/hips, overall movement severity, incapacitation, participant awareness). Facial and oral movements (items 1 through 4), extremity movements (items 5 and 6), and trunk movements (item 7) were observed unobtrusively while participant was at rest (e.g., in waiting room), and study physician would make global judgments on participant's dyskinesia's (items 8 through 10). Each item was rated on 5-point scale of severity from 0 (none) to 4 (severe) and assessment of problems with teeth or dentures (yes = 1, no = 0) and if the participant normally wears dentures (yes = 1, no = 0). Total score ranged from 0 to 42. Higher scores indicated worst outcome.

SP: Participants who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

The BARS consisted of 4 items related to akathisia: objective observation of akathisia by the investigator, subjective feelings of restlessness by the participant, subjective distress due to akathisia, and global clinical assessment of akathisia. The global clinical evaluation was made on a 6-point scale, with zero representing absence of symptoms and a score of 5 representing severe akathisia.

Safety population included those participants in who received at least 1 dose of study drug (brexpiprazole or placebo). Overall number of participants analyzed = number of participants with data available for analysis for this outcome measure. Number analyzed = number of participants with data available for analyses at the specified time point.

Suicidality was monitored using the C-SSRS. Suicidality was defined as at least one occurrence of suicidal ideation (including wish to be dead, non-specific suicidal thought, suicidal ideation-no intent, ideation with intent, no plan, ideation with plan/intent) or at least one occurrence of suicidal behavior (actual attempt, non-suicidal self-injurious behavior, interrupted attempt, aborted attempt, preparatory acts/behavior, suicidal behavior) for the assessment period.

Safety population included those participants who received at least 1 dose of study drug (brexpiprazole or placebo).