Marijuana is the most commonly used illicit drug in the United Kingdom (with 11% of 16-59 years olds having used it in the last year; see ref. 78) and United States. It is obtained from the Cannabis sativa plant, and the principal active ingredient, accounting for the majority of effects, is A-9-tetrahydrocan-nabinol (THC). There are several forms, including hashish (a resin), herbal cannabis (a green-colored preparation made from the leaves of the plant), and cannabis oil. "Skunk" is a term used to describe a potent form of the cannabis plant with high levels of THC (79), which is grown indoors using hydroponic techniques, in nutrient-rich liquids rather than soil, under grow lights, or in greenhouse conditions. The onset of effects is reported as being more rapid, and the hallucinogenic properties are heightened. Psychotic episodes may be precipitated by relatively small quantities (80).
Cannabis is usually smoked but can be ingested as "cannabis cookies." One "joint" typically contains 10-30 mg of THC and has an onset of action of 10-20 minutes, with effects lasting 2-3 hours (50). The acute effects of cannabis are given in Table 13 (81).
Tolerance develops to many effects of cannabis, including the "high" with chronic use, and an abstinence syndrome has been described with disturbed sleep, decreased appetite, restlessness, irritability, and sweating. Withdrawal symptoms are usually mild and short-lived, although they may be more severe in heavy regular users (82).
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