Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist. At high, fully anesthetic level doses, ketamine has also been found to bind to opioid μ receptors type 2 in cultured human neuroblastoma cells, however without agonist activity, and to sigma receptors in rats. Also, ketamine interacts with muscarinic receptors, descending monoaminergic pain pathways and voltage-gated calcium channels. Like other drugs of this class such as tiletamine and phencyclidine (PCP), it induces a state referred to as “dissociative anesthesia” and is used as a recreational drug.

Ketamine is sold in either powdered or liquid form. In its powdered form it can be insufflated (inhaled), injected, or taken orally (though this works as a laxative). The smoke has a distinctive bitter taste but the onset of the high is much faster than when ingested or injected intramuscularly (IM), however the effects dissipate quickly. Ketamine is typically injected into the leg, the onset for IM is about one minute. Heavy ketamine users solely use IM as their primary method of administration due to the bypassing of the liver, its increased efficiency, and smoother high. Oral use usually requires more material, but results in a longer trip. However, when administered orally, ketamine is rapidly metabolised to norketamine, which possesses sedating effects; this route of administration is unlikely to produce a dissociative state characteristic of ketamine unless very high doses (500 mg+) are ingested.

Ketamine produces effects similar to phencyclidine (PCP) and dextromethorphan (DXM). Unlike the other well known dissociatives PCP and DXM, ketamine is very short acting, its hallucinatory effects lasting sixty minutes when insufflated or injected and up to two hours when ingested, the total experience lasting no more than a couple of hours. Like other dissociative anaesthetics, hallucinations caused by ketamine are fundamentally different from those caused by tryptamines and phenethylamines. At low doses, hallucinations are only seen when one is in a dark room with one’s eyes closed, while at medium to high doses the effects are far more intense and obvious.

References: http://en.wikipedia.org/wiki/Ketamine