Kaposi's sarcoma: a form of cancer that usually erupts as purple splotches on the skin. It is considered to be an opportunistic disease that is one of the signs of AIDS.

Keeley Institute: a series of 118 treatment centers in the United States that treated alcoholics, drug addicts, and tobacco smokers between 1880 and 1920.

ketamine: used as a recreational club drug, it is an anesthetic that produces catatonia and deep analgesia; side effects include excess saliva, dysphoria, and hallucinations. Its chemistry and effects are very similar to PCP.

khat: a 10-20 foot shrub whose active ingredient is cathinone, a mild-to-medium stimulant. It is brewed in a tea or the leaves can be chewed and the active ingredient absorbed. It is popular in Somalia, East Africa, Yemen, and other Middle Eastern countries.

kilogram: a metric unit of weight that equals 2.2 pounds.

kindling: see inverse tolerance.

Klonopin®: clonazepam; a popular benzodiazepine sedative. People in methadone maintenance use it to increase the high from methadone.

knockout drops: old street term for chloral hydrate, a sedative hypnotic.

kola nut: the seeds of the Cola nitida tree found in Africa. It contains a high concentration of caffeine.

Korsakoff's psychosis: see Korsakoff's syndrome.

Korsakoff's syndrome: a disease that most often affects heavy, long-term drinkers; symptoms include short-term memory failure, confusion, emotional apathy, and disorientation.

krystal: street name for PCP; not to be confused with the street terms "crystal" or "crystal meth" that denote methamphetamine.