4. Effects on Man of Using Cannabis

It is now generally believed that A9-THC accounts for a large part of the pharmacological activity of cannabis preparations (see section 2.1). The percentage of A9-THC in cannabis preparations varies markedly (see section 3.1). To a large extent, the potency of various preparations varies directly with their A9-THC concentration. Because A9-THC is insoluble in water, the only practical routes of administration in man, as yet, are by ingestion and by inhalation of smoke (see section 3.1). In medicine and in much of the older experimental work, cannabis was administered orally as a concentrated and biologically standardized alcoholic extract. To obtain the maximum effect from cannabis preparations they must be smoked by a technique that is somewhat different from that of smoking tobacco cigarettes and must be learned by practice.1 When this tech-nique is followed, about 50 % of the A9-THC in marhuana comes over in the smoke and most of the remainder is converted to CBN or CBD or both (Manno et al., 1970). Exhaled air contains practically no A9-THC when the specified technique is used. It is thus assumed that roughly 50 % of the A9-THC content of a marihuana cigarette is absorbed by the lungs and con-stitutes the dosage actually delivered to the smoker (Manno et al., 1970). Available data on the amounts of A9-THC deliveredby smoking arerelatively meagre; more research is needed on the variations in the dosage obtained from marihuana and other cannabis preparations when different smoldng devices and techniques are used. A9-THC is about 3 times as potent when smoked as when ingested (Isbell et al., 1967). The subjective effect begins very rapidly when A9-THC or cannabis preparations are smoked, an experienced smoker being able to perceive subjective effects within a minute after one or two puffs of a potent preparation. The peak effects are probably reached within 20-30 minutes after smoking. In contrast, when A9-THC or extracts of cannabis are taken orally, about 30 minutes elapse before subjective effects are perceived. The duration of action varies with the dose, but the effects of a single administration are usually dissipated 3-4 hours after smoking or about 8 hours after oral administration.' The degree and duration of effect after smoking a given amount also probably vary with the speed of smoking.