n. a drug that is closely related to PCP (phencyclidine). It acts as an antagonist at NMDA receptors and was formerly used as a dissociative anesthetic. Disorientation and perceptual distortions may result from its use, which have limited its utility in surgical anesthesia and made it a sought-after drug of abuse. It is ingested in the form of tablets, capsules, or powder by drug users for its hallucinogenic effects. Low-dose intravenous infusions have been reported to improve symptoms in patients with treatment-resistant unipolar and bipolar depression. U.S. trade name: Ketalar.