Overview: Ketamine is the drug flavor-of-the-month in much of the United States and Europe right now, particularly among dance-club devotees and ravers. As drugs-of-the-month go, they could have picked a better one. Developed as a surgical anesthetic, K adds in a twist of hallucinogenic effects, much like its better-known chemical cousin and pharmacological predecessor, PCP. And its weird mix of effects is also earning it a reputation for being every bit as unpredictable.

Street names: K, Special K, Vitamin K.

Appearance: Although pharmaceutical ketamine is liquid, it's often microwaved until dry, then crushed into a powder.

Actions/Effects: In the brain, ketamine acts at the same receptor sites as PCP, and alters the function of several neurotransmitter systems. Drug effects come on fast, usually within 15 seconds of injection or inhalation. After a brief period (10-15 minutes) of unconsciousness and a longer period (30-40 minutes) of anesthesia, users commonly report intense hallucinations, depersonalization, out-of-body experiences, and bizarre or mystical experiences.

Side Effects/Risks: Common side effects include muscle spasm, blurred vision, dizziness, slurred speech, respiratory depression, and impaired coordination. Visual "flashbacks" are sometimes reported days or weeks after use. Also, amnesia, aggressive behavior, and paranoid or delusional thinking sometimes occur.

Duration: Depends on dose. Impaired thinking may persist for hours.

Addiction Potential: Tolerance to effects builds quickly, and habituation is possible.

Medical Uses: Although ketamine was developed as a surgical anesthetic, the "emergence" reactions it triggers on awakening limited its acceptance. Today, it's mostly used in surgery involving children (who report fewer side effects), and for veterinary procedures.

Legal Issues: For years, ketamine was not a controlled substance, but was placed under Schedule III of the Controlled Substance Act by the Drug Enforcement Administration in August, 1999. Several states have also increased penalties for its possession and distribution.

Trends: Like many previous holders of drug-of-the-month status, ketamine is better-known than it is commonly-used. Interest in it seems at least partly fueled by media coverage, since only 1.6 percent of the high school class of 2005 reported any use of it during the previous year.