<unk>  (a contraction of the chemical name phenylcyclohexylpiperidine), abbreviated<unk> , is a dissociative drug formerly used as an anesthetic agent, exhibiting hallucinogenic and neurotoxic effects.[citation needed]
It was first patented in 1952 by the Parke-Davis pharmaceutical company and marketed under the brand name Sernyl.<unk>  is listed as a Schedule II drug in the United States under the Convention on Psychotropic Substances.
In chemical structure,<unk>  is an arylcyclohexylamine derivative, and, in  pharmacology, it is a member of the family of dissociative anesthetics.<unk>  works primarily as an NMDA receptor antagonist, which blocks the activity of the NMDA Receptor. Other NMDA receptor antagonists include ketamine, tiletamine, and dextromethorphan. Although the primary psychoactive effects of the drug last only hours, total elimination from the body is prolonged, typically extending over weeks.
More than 30 different analogues of<unk>  were reported as being used on the street during the 1970s and 1980s, mainly in the USA. The best known of these are<unk> y (Rolicyclidine, 1-(1-phenylcyclohexyl)pyrrolidine); PCE (Eticyclidine, N-ethyl-1-phenylcyclohexylamine); and TCP (Tenocyclidine, 1-(1-(2-Thienyl)cyclohexyl)piperidine). These compounds were never widely-used and did not seem to be as well-accepted by users as<unk>  itself, however they were all added onto Schedule I of the Controlled Substance Act because of their putative similar effects.
The generalised structural motif required for<unk> -like activity is derived from structure-activity relationship studies of<unk>  analogues, and summarised below. All of these analogues would have somewhat similar effects to<unk>  itself, although, with a range of potencies and varying mixtures of anaesthetic, dissociative and stimulant effects depending on the particular substituents used. In some countries such as the USA, Australia, and New Zealand, all of these compounds would be considered controlled substance analogues of<unk> , and are hence illegal drugs, even though many of them have never been made or tested.
Phencyclidine
Benzidine
Benzocaine 
Cannabis 
Heroin
Methamphetamine
Benzphetamine
Opiate