A Study of Ketamine as an Antidepressant

This clinical study consists of two phases. In Phase I, participants will receive variable doses of intravenous, intramuscular, or subcutaneous ketamine (0.1-0.5mg/kg) or placebo (saline, or 0.01mg/kg midazolam) weekly for up to 6 consecutive weeks. Prior to receiving ketamine/placebo, participants' mood and psychiatric symptoms will be assessed. Once they have received their treatment, mood, psychiatric side effects, ketamine blood levels, heart rate, blood pressure and biomarkers will be assessed. Mood and cognitive performance be assessed again after 4 hours. Finally, mood will also be assessed the next day. Some participants may be eligible to continue to Phase II. In this phase, participants will receive doses of ketamine approximately weekly for up to 6 months. During this phase, participants' mood, psychiatric, biomarkers and cognitive outcomes will be assessed. The purpose of the trial is to investigate the antidepressant and safety effects of using ketamine as a treatment in depression.