Early Effects of Ketamine vs Placebo With Venlafaxine in Severe Depression Patients

This study is testing whether a low-dose infusion of ketamine given at the start of treatment can speed up relief of severe depression in hospitalized patients who are also being started on venlafaxine (a standard antidepressant). The study compares ketamine against a placebo infusion, with both groups also receiving venlafaxine. **You may be eligible if...** - You are between 18 and 65 years old - You have been hospitalized for a severe episode of major depression (not bipolar depression) with a high depression score - Your doctors have decided to start you on venlafaxine as treatment - You have signed informed consent and have health insurance - If you are a woman of childbearing age, you are using effective contraception **You may NOT be eligible if...** - You have bipolar disorder, schizophrenia, or a personality disorder - You have a history of substance abuse or dependence - You are currently using certain other psychiatric medications that cannot be stopped - You are pregnant or breastfeeding - You have severe heart, liver, or kidney disease Talk to your doctor to see if this trial is right for you.