The purpose of this study is to evaluate the safety and effectiveness of JNJ-18038683 compared to escitalopram and placebo in patients with moderate to severe depression.

This study is being done to assess safety and tolerability and to explore the effectiveness of a new, experimental drug in the treatment of moderate to severe depression. Approximately 225 patients with depression will be recruited for the study. Patients who meet study criteria will need to stop takng any depression medications they are currently using. They will be randomly assigned to one of 3 treatment arms; each patient has an equal chance of receiving 20 mg JNJ-18038683, 20 mg escitalopram, or placebo. Placebo has no active drug. Escitalopram is a drug currently approved to treat depression. This is a blinded study, i.e. the patient, the study doctor and the study sponsor will not know what treatment the patient receives until all patients complete the study. Patients receiving either escitalopram or JNJ-18038683 will be titrated up to their assigned dose, receiving 10 mg doses for one week prior to increasing to 20 mg. Patients who are not able to tolerate 20 mg of JNJ-18038683 will be allowed to drop down to the 10 mg dose at any time after the titration period. Patients taking 20 mg escitalopram will receive 10 mg their final week to taper off of the drug. Patients will be dispensed a drug blister card at each weekly visit containing drug for the upcoming week. The study doctor and the sponsor will monitor the study for the occurrence of possible side effects. In addition to a screening visit, patients will return weekly for 9 additional study visits. After completing the study, patients may resume other depression medications. Medical and psychiatric history, physical examination, blood pressure, heart rate, temperature, weight and ECGs will be checked periodically. Blood samples will be taken for standard safety laboratory tests as well as for the measurement of the drug blood level. Questionnaires relating to depression, sleep and sexual experience will be administered throughout the study.

Each day for nine weeks, patients will take orally two JNJ-18038683 tablets, active and/or placebo, and two escitalopram capsules, active and/or placebo.

Inclusion Criteria:

• Diagnosed with moderate to severe major depressive disorder
• Willing to use acceptable methods of birth control throughout the study and for 3 months after
• In good general health

Exclusion Criteria:

• No history or current diagnosis of other psychiatric conditions such as bipolar disorder, psychotic disorder, general anxiety disorder, anorexia, obsessive compulsive disorder, post traumatic stress disorder, antisocial personality disorder, mental retardation, pervasive developmental disorder, or cognitive disorder
• No history or presence of drug abuse
• No use of prescription medications or herbal medications other than hormone replacement therapies
• No prior history of heart disease or current significant blood, lung, kidney, liver, heart, breathing, neurologic or thyroid disorders
• No patients who are either pregnant or nursing