A Study of Flexible or Fixed Dose LY2216684 as Adjunctive Treatment for Participants With Major Depressive Disorder Who Have Had a Partial Response to Selective Serotonin Reuptake Inhibitor (SSRI) Treatment

The purpose of this study is to assess if LY2216684 (flexible dose of 12 to 18 milligrams \[mg\] or fixed dose of 6 mg once daily) is superior to placebo once daily in the adjunctive treatment of participants with Major Depressive Disorder (MDD) who were identified as partial responders to an adequate course of treatment with a selective serotonin reuptake inhibitor (SSRI) during an 8-week, double-blind, acute adjunctive treatment phase.

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:

* Clinical diagnosis of Major Depressive Disorder (MDD)
* Using a reliable method of birth control
* Are taking a selective serotonin reuptake inhibitor (SSRI) approved for MDD treatment within the participant's country and the SSRI prescribed, including dose, should be consistent with labeling guidelines within the participating country
* Have a partial response to SSRI treatment
* Meet inclusion scores on pre-defined psychiatric scales to assess diagnosis of depression, disease severity, and response to SSRI treatment
* Reliable and able to keep all scheduled appointments

Exclusion Criteria:

* Presence of another primary psychiatric illness:

  * Have had or currently have any additional ongoing Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (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, post-traumatic stress disorder, generalized anxiety disorder, 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 1 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
* Have any diagnosed medical condition that could be exacerbated by noradrenergic agents, including unstable hypertension, unstable heart disease, tachycardia, tachyarrhythmia, narrow-angle glaucoma, and history of urinary hesitation or retention
* Use of excluded concomitant or psychotropic medication other than SSRI
* Have initiated or discontinued hormone therapy within the previous 3 months of 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
* Enrollment in a clinical study for an investigational drug
* Serious or unstable medical condition
* History of seizure disorders
* Have initiated psychotherapy, change in intensity of psychotherapy or other nondrug therapies (such as acupuncture or hypnosis) within 6 weeks prior to enrollment or any time during the study
* Participants who, in the opinion of the investigator, are judged to be at serious risk for harm to self or others