- History of recreational ketamine use, recreational PCP use, or an adverse reaction to ketamine. Subjects who have participated prior research ketamine studies will be eligible providing they have participated in no more than 5 previous research ketamine infusions. Subjects can have infusions not more frequently than biweekly and not more than 1/month on average, therefore subjects entering the study will need to wait 1 month if they had a single infusion and 6 weeks if they have had two closely spaced infusions.