A Study in Participants With Major Depressive Disorder (MDD) With Anhedonia and Inadequate Response to Current Antidepressant Therapy Including a Selective Serotonin Reuptake Inhibitor (SSRI) or Serotonin Norepinephrine Reuptake Inhibitor (SNRI)

Inclusion Criteria:

• Meets the diagnostic criteria for single episode or recurrent major depressivedisorder (MDD) without psychotic features, according to either the tenth revision ofthe International Statistical Classification of Diseases and Related Health Problems (ICD-10) or the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)

• Is considered to suffer from a moderate or severe depressive syndrome, as defined bya Montgomery-Asberg Depression Rating Scale (MADRS) total score greater than orequal to (>=) 22 at entry

• Is initiating or is planning to initiate a new add-on antidepressant treatment perlocal prescribing information to treat the current depressive episode. In thecontext of this observational study, a new add-on antidepressant treatment isconsidered any new pharmacological or non-pharmacological treatment that isprescribed in addition to the current antidepressant treatment, inclusive of anselective serotonin reuptake inhibitor/serotonin norepinephrine reuptake inhibitor (SSRI or SNRI) with the intent to improve a participant's clinical depressivesyndrome. Accordingly, any dose escalation of an antidepressant prescribed prior tobaseline or the addition of any drug intended to increase the plasma-concentrationof an antidepressant prescribed prior to baseline is not considered a newantidepressant treatment; In parallel with the inclusion of participants consideredfor add-on strategy, in the United States only, a cohort of approximately 50participants who switch to a new single (monotherapy) pharmacological antidepressantagent of any antidepressant class per local prescribing information to replace thecurrent antidepressant treatment (that is, "monotherapy switch strategy") will beenrolled. The enrollment of participants with switch to monotherapy will bemonitored, and sites will be notified by the sponsor once the planned number for thecohort is achieved. Thereafter, only add-on strategy participants will be enrolled

• Must be capable of providing informed consent (for example, able to read and write),based on the opinion of the participating physician. Must sign (or their legallyacceptable representative) an informed consent form indicating that he or sheunderstands the purpose of the study and that he or she agrees to have their datacollected and analyzed, in accordance with local requirements and the study protocol

• Meets the criterion for inadequate response to a current antidepressant treatmentthat includes an SSRI or SNRI (monotherapy SSRI, monotherapy SNRI, combination ofantidepressants that includes SSRI/SNRI or SSRI/SNRI augmentation), administered atan adequate dose (as defined in the Massachusetts General Hospital - AntidepressantTreatment Response Questionnaire [MGH ATRQ]) and duration (at least 6 weeks) in thecurrent episode of depression

Exclusion Criteria:

• Has a current or prior diagnosis of a psychotic disorder, MDD with psychoticfeatures, bipolar or related disorders or intellectual disability, according toDSM-5 or ICD-10

• Participants who require an antidepressant (SSRI/SNRI) change (switch to anotherantidepressant monotherapy), except for a limited number of participants to berecruited in the United States only

• Unstable general medical condition (for example, cardiovascular, respiratory,gastrointestinal, neurologic, hematologic, rheumatologic, immunologic, or endocrinedisorders) in the past 3 months that would compromise participation and normalroutine medical care per the physician's clinical judgment

• Has lack of treatment response to the current antidepressant therapy that includes aSSRI/SNRI (that is, no [0%] symptomatic improvement despite adequate dose andduration of the antidepressant treatment) assessed using the MGH ATRQ

• History of dementia or mild cognitive impairment. Physician's clinical judgmentshould document that participant is capable of complying with observational studyrequirements and being able to complete the appropriate scales

• Has homicidal ideation/intent or is at imminent risk of suicide per the physician'sclinical judgment and/or based on the Columbia Suicide Severity Rating Scale (C-SSRS) corresponding to a response of "Yes" on Item 4 (active suicidal ideationwith some intent to act, without specific plan) or Item 5 (active suicidal ideationwith specific plan and intent)