Safety and Efficacy of MK-6096 as Adjunctive Therapy in Participants With Major Depressive Disorder And Partial Response to Antidepressant Monotherapy (MK-6096-022 AM3)

Participants will continue to take their pretrial antidepressant medication as prescribed
throughout the trial. Participants will be randomized in a 1:1 ratio to receive MK-6096 or
placebo for a 6-week treatment period. Following completion of the treatment period,
participants will enter a 2-week double-blind run-out period. During the run-out period,
participants who received placebo in the 6-week treatment period will continue to receive
placebo and participants who received MK-6096 in the 6-week treatment period will receive
either MK-6096 or placebo in a 1:1 ratio.

Key Inclusion Criteria:

- Male, female not of reproductive potential, or female of reproductive potential who
is not pregnant and agrees to use acceptable contraception

- Current primary diagnosis of recurrent major depressive disorder,

without psychotic features, with a current moderate or severe depressive episode

- Duration of the current major depressive episode must be at least 2 months

but no more than 18 months at Screening

- Participant has undergone an adequate trial of an antidepressant (one of identified
SSRIs or SNRIs, or bupropion) for the current depressive episode

Key Exclusion Criteria:

- Current primary psychiatric diagnosis other than major depression

- Lifetime diagnosis of bipolar disorder, schizophrenia, schizoaffective

disorder, or other psychotic disorder

- Alcohol or other substance abuse or dependence (excluding nicotine)

- Clinically significant abnormality or disease of the central nervous system
(including dementia and other cognitive disorders or traumatic brain injury)

- Imminent risk of self-harm or of harm to others

- Participant is a psychiatric inpatient

- Participant has been on continuous antidepressant treatment for >18 months prior to
Screening visit

- Inadequate response to more than 3 adequate antidepressant trials (including the
current antidepressant treatment trial) for treatment of the current depressive
episode

- Participant ever received electroconvulsive therapy, transcranial magnetic
stimulation, or vagal nerve stimulation for treatment of depression

- History of narcolepsy, cataplexy, circadian rhythm disorder, parasomnia,
sleep-related breathing disorder, restless legs syndrome, periodic limb movement
disorder, excessive daytime sleepiness or difficulty sleeping due to a medical
condition

- Clinical, laboratory, or electrocardiogram (ECG) evidence of significant systemic
disease

- Cardiovascular event (e.g., myocardial infarction) or procedure (e.g., coronary
artery bypass surgery) within 3 months of study

- History of malignancy ≤5 years prior to study, except for adequately treated basal
cell or squamous cell skin cancer or in situ cervical cancer

- Body Mass Index >40 kg/m^2

- Pregnancy, breast-feeding, or expecting to become pregnant