The Objective of This Study is to Evaluate the Efficacy, Safety and Tolerability of Cariprazine as an Adjunctive Treatment to Antidepressant Therapy (ADT) in Patients With Major Depressive Disorder (MDD) Who Have Had an Inadequate Response to Antidepressants Alone

Inclusion Criteria: * Written informed consent has been obtained. * Written documentation has been obtained in accordance with the relevant country and local privacy requirements, where applicable (eg, Written Authorization for Use and Release of Health and Research Study Information \[US sites\] and written Data Protection consent \[EU sites\]). * Participant must be an outpatient at the time of Visit 1 (Screening). * Participant meets the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for MDD based on Structured Clinical Interview for DSM-5 (SCID-5), with a current major depressive episode of at least 8 weeks and not exceeding 24 months in duration at Visit 1/Screening. A diagnosis of MDD with psychotic features will be acceptable. * Diagnosis of MDD confirmed through a formal adjudication process. * Participant demonstrates ability to follow study instructions and likely to complete all required visits. * Participant must have an inadequate response, as measured by the modified antidepressant treatment response questionnaire (ATRQ), to 1 to 3 antidepressants administered during the current episode at an adequate dose (as per package insert) and for at least 6 weeks duration, with at least one dose escalation during the current depressive episode. * Only one antidepressant (of sufficient dose per package insert and taken for at least 6 weeks) will be allowed at randomization and Participants must agree to continue taking the same ADT dosing regimen through completion of Visit 6/early termination (ET). Participants who are taking more than one antidepressant at Screening, regardless of the indication, will need to discontinue all other antidepressants prior to Visit 2 (Baseline). * Male and female Participants must agree to use a medically acceptable and highly effective method of birth control during the course of the entire study. * Women of childbearing potential (only) must have a negative serum β-human chorionic gonadotropin pregnancy test prior to Visit 2. Exclusion Criteria: * Diagnosis of any current psychiatric diagnosis other than MDD (including those with current intellectual development disability) with the exception of specific phobias. * Participant has a history of intolerance or hypersensitivity to cariprazine or other drugs of the same class or to rescue medications.