Ketamine Trial for the Treatment of Depression

Individuals will be eligible for enrolment on the basis of: * major depressive disorder for at least three months duration * an inadequate response to at least 2 adequate antidepressants * MADRS ≥ 20 Patients will be excluded on the basis of: * History of psychosis * History of bipolar disorder * Any unstable medical or neurologic condition * Any Axis I disorder other than MDD judged to be primary presenting problem * Planned major changes to psychotropic medication * Significant risk of suicide * Planned or probable use of ECT * Age under 16 years, or 16-17 years without parental consent * Substance abuse or dependence in previous 6 months * Any history of abuse of ketamine or phencyclidine * Contraindication to the use of ketamine * Planned use of ketamine * Women of childbearing potential not taking reliable contraception * Likely non-compliance with trial treatment * Other condition judged by the treating clinician as likely to impact on the ability of the participant to complete the trial