Patients currently taking psychiatric medications may continue them during the study. However, if a patient is taking a benzodiazepine (such as Ativan, Klonopin, or Xanax), they will be able to take up to 2mg per day of Lorazepam during the week before the infusion, but none will be permitted in the 24 hours pre-infusion. Also, Zolpidem (Ambien) will not be permitted in the 24 hours pre-infusion. If a person chooses to participate, their dose of benzodiazepine may need to be reduced so that they can do without it during the 24 hours pre-infusion.

Participants are randomly assigned to receive a single dose of Ketamine (0.5 mg/kg) or Midazolam (0.02 mg/kg), which is given slowly, in a vein, over about 40 minutes. The study is "double-blind," meaning patients and study staff will not know which medication is in the infusion.

If a patient does not respond to the first infusion, and s/he received Midazolam, then s/he will be offered the option of a second infusion, this time with Ketamine (0.5 mg/kg). After the infusion(s), participants will have weekly research interviews for 6 weeks to monitor response.

After post-infusion research measures are completed, all subjects will receive open clinical treatment. During open clinical treatment, medication will be changed for those patients who don't respond or whose response is transient.

Participation in this study requires a brief inpatient stay, at no cost, at the New York State Psychiatric Institute (NYSPI).

Eligible participants enrolled in this study will be offered medication management visits at no cost for a total of up to 6 months combining inpatient and outpatient treatment. At the end of the 6 months of treatment patients will be referred for ongoing care.