A Study in Participants With Major Depressive Disorder Who Are Partial Responders to Selective Serotonin Reuptake Inhibitor

The primary objective of this study is to assess whether LY2216684 12 milligrams (mg) or 18 mg flexible dose once daily is superior to placebo once daily in the adjunctive treatment of participants with major depressive disorder (MDD) who are partial responders to their selective serotonin reuptake inhibitor (SSRI) treatment.

Following the Confirmation (CF) Phase, participants were randomized to adjunctive LY2216684 or adjunctive placebo if they had \<25% improvement in the Montgomery-Åsberg Depression Rating Scale (MADRS) total score over the past 3 weeks and a current MADRS total score ≥14. Participants who did not meet criteria received adjunctive placebo to preserve the blind.

Eligibility Criteria:
Inclusion Criteria:

* Women of child-bearing potential may participate but must test negative for pregnancy at the time of study entry; both women/men agree to use a reliable method of birth control
* Are being treated with one of the following selective serotonin reuptake inhibitors (SSRIs): escitalopram, citalopram, sertraline, fluoxetine, paroxetine, or fluvoxamine; for at least 6 weeks prior to investigational product dispensing with at least the last 4 weeks at a stable, optimized dose
* Drug and dosage should be within the labeling guidelines for the specific country
* Meet criteria for major depressive disorder (MDD), as defined by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision® (DSM-IV-TR) criteria
* Meet criteria for partial response, as defined by investigator's opinion that the participant has experienced a minimal clinically meaningful improvement with SSRI
* Have a GRID 17-Item Hamilton Depression Rating Scale (GRID-HAMD17) total score greater than or equal to 16 at screening
* Have less than or equal to 75% improvement on the current SSRI at screening determined by the Massachusetts General Hospital Antidepressant Treatment Response Questionnaire (MGH-ATRQ)

Exclusion Criteria:

* Have had or currently have any additional ongoing DSM-IV-TR Axis 1 condition other than major depression within 1 year of screening
* Have had any anxiety disorder that was considered a primary diagnosis within the past year (including panic disorder, obsessive-compulsive disorder \[OCD\], post-traumatic stress disorder \[PTSD\], generalized anxiety disorder \[GAD\], and social phobia, but excluding specific phobias)
* Have a current or previous diagnosis of a bipolar disorder, schizophrenia, or other psychotic disorder
* Have a history of substance abuse and/or dependence within the past year (drug categories defined by DSM-IV-TR), not including caffeine and nicotine
* Have an Axis II disorder that, in the judgment of the investigator, would interfere with compliance with protocol
* Unstable medical conditions that contraindicate the use of LY2216684
* Have any diagnosed medical condition that could be exacerbated by noradrenergic agents, including unstable hypertension, unstable heart disease, tachycardia, tachyarrhythmia, narrow-angled glaucoma, history of urinary hesitancy or retention
* Use of excluded concomitant or psychotropic medication other than SSRI
* Have initiated or discontinued hormone therapy within the 3 months prior to enrollment
* History of treatment-resistant depression as shown by lack of response of the current depressive episode to 2 or more adequate courses of antidepressant therapy at a clinically appropriate dose for at least 4 weeks or, in the judgment of the investigator, the participant has treatment-resistant depression
* Have a lifetime history of vagal nerve stimulation (VNS), transcranial magnetic stimulation (TMS), or psychosurgery
* Have received electroconvulsive therapy (ECT) in the past year