Cannabis is obtained from the annual plant Cannabis sativa (hemp) and its varieties Cannabis indica and Cannabis americana. The preparations that are smoked are called marijuana (grass, pot, weed, etc.) and consist of crushed leaves and flowers. There is a wide variety of regional names, e.g. ganja (India, Caribbean), kif (Morocco), dagga (Africa). The resin scraped off the plant is known as hashish (hash). The term cannabis is used to include all the above preparations. Since most preparations are illegally prepared it is not surprising that they are impure and of variable potency. The plant grows wild in the Americas,38 Africa and Asia. It can also be grown successfully in the open in the warmer southern areas of Britain.


Of the scores of chemical compounds that the resin contains, the most important are the oily cannabinoids, including tetrahydrocannabinol (THC), which is the chief cause of the psychic action. Samples of resin vary greatly in the amounts and proportions of these cannabinoids according to their country of origin; as the sample ages, its THC content declines. As a result, the THC content of samples can vary from almost zero to 8%.

Smoke from a cannabis cigarette (the usual mode of use is to inhale and hold the breath to allow maximum absorption) delivers 25-50% of the THC content to the respiratory tract.

38 The commonest pollen in the air of San Francisco,

California is said to be that of the cannabis plant, illegally cultivated.

THC (t'/2 4 d) and other cannabinoids undergo extensive biotransformation in the body, yielding scores of metabolites, several of which are themselves psychoactive. They are extremely lipid-soluble and are stored in body fat from which they are slowly released.39 Hepatic drug metabolising enzymes are inhibited acutely but may also be induced by chronic use of crude preparations.


The discovery of cannabinoid CBj-receptors (expressed by central and peripheral neurones) and CB2-receptors (expressed by immune cells) and the presence of endogenous agonists will point the way to identifying its mechanisms of action, although these are as yet not well understood.

Psychological reactions are very varied, being much influenced by the behaviour of the group. They commence within minutes of starting to smoke and last 2-3 h. Euphoria is common, though not invariable, with giggling or laughter which can seem pointless to an observer. Sensations become more vivid, especially visual, and contrast and intensity of colour can increase, although no change in acuity occurs. Size of objects and distance are distorted. Sense of time can disappear altogether, leaving a sometimes distressing sense of time-lessness. Recent memory and selective attention are impaired; the beginning of a sentence may be forgotten before it is finished, and the subject is very suggestible and easily distracted. Psychological tests such as mental arithmetic, digit-symbol substitution and pursuit meter tests show impairment. These effects may be accompanied by feelings of deep insight and truth. Memory defect may persist for weeks after abstinence.

Once memory is impaired, concentration becomes less effective, since the object of attention is less well remembered. With this may go an insensitivity to danger or the consequences of actions.

A striking phenomenon is the intermittent wavelike nature of these effects which affects mood,

39 When a chronic user discontinues, cannabinoids remain detectable in the urine for an average of 4 weeks and it can be as long as 11 weeks before 10 consecutive daily tests are negative (Ellis G M et al 1986 Clinical Pharmacology and Therapeutics 38: 572).

visual impressions, time sense, spatial sense, and other functions.

The desired effects of cannabinoids, as of other psychodysleptics, depend not only on the expectation of the user and the dose, but also on the environmental situation and personality. Genial or revelatory experiences may indeed occur, e.g. 'Haschich Fudge'.40

(which anyone can whip up on a rainy day). This is the food of Paradise ... euphoria and brilliant storms of laughter, ecstatic reveries and extension of one's personality on several simultaneous planes are to be complacently expected. Almost anything St Teresa41 did, you can do better...

But this cannot be relied on. The effects can be unpleasant, especially in inexperienced subjects, particularly timelessness and the feeling of loss of control of mental processes. Feelings of unease, sometimes amounting to anguish and acute panic occur as well as 'flashbacks' of previously experienced hallucinations, e.g. on LSD. There is also, especially in the habitual user, a tendency to paranoid thinking. High or habitual use can be followed by a psychotic state; this is usually reversible, quickly with brief periods of cannabis use, but more slowly after sustained exposures. Evidence suggests that chronic use may precipitate schizophrenia in vulnerable individuals.

The effect of an acute dose usually ends in drowsiness and sleep. It is claimed that death has not occurred.

Tolerance, with continued heavy use, and a withdrawal syndrome occur (depression, anxiety, sleep disturbance, tremor and other symptoms). Many users find it very difficult to abandon cannabis. In studies of self-administration by monkeys, spontaneous use did not occur but, once use was initiated, drug-seeking behaviour developed. Subjects who have become tolerant to LSD or opioids as a result of repeated dosage respond normally to cannabis but

40 From The Alice B Toklas cook book 1954 Michael Joseph, London. The author was companion to Gertrude ('rose is a rose is a rose') Stein (1874-1946).

41 St Teresa of Avila (1515-82) was noted for her power of lévitation.

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