Efficacy and Safety Study of ABT-436 in Major Depressive Disorder

Inclusion Criteria:

• Has a primary Diagnostic and Statistical Manual of Mental Disorders-FourthEdition-Text Revision diagnosis of major depressive disorder without psychoticfeatures

• No current antidepressant treatment within 7 half-lives or 2 weeks, whichever islonger, prior to Day minus 1.

• Can safely be treated on an outpatient basis.

• A condition of general good physical health.

• Surgically sterile, using a highly effective method of birth control or (if female) atleast 1 year post menopausal.

Exclusion Criteria:

• History of hypersensitivity, intolerance or adverse reaction to escitalopram that ledto discontinuation, or hypersensitivity to citalopram. History of serotonin syndrome.

• Inadequate response to more than two different antidepressant medications during thecurrent major depressive episode.

• History of electroconvulsive therapy, vagal nerve stimulation or deep brainstimulation.

• History of transcranial magnetic stimulation during the current major depressiveepisode.

• Psychotherapy that has not been ongoing for at least 3 months prior to Day minus 1.