The health and psychological consequences of cannabis use - chapter 9

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9. An overall appraisal of the health and psychological effects of cannabis

9.2 Two special concerns

Two issues which have hitherto been ignored require brief discussion. These are the possible health implications of: the storage of THC in body tissue; and any increases in the average potency of cannabis products (as indexed by THC content) that may have occurred in recent decades.

9.2.1 Storage of THC

There is good evidence that with repeated dosing of cannabis at frequent intervals, THC can accumulate in fatty tissues in the human body where it may remain for considerable periods of time (see above pp34-35). Attitudes towards this fact are strongly coloured by the perceiver's views about cannabis use: those who are opposed to its use usually regard this as a cause for major concern; proponents of cannabis use largely ignore it. There is no evidence to make a confident judgment one way or the other. The storage of cannabinoids would be serious cause for concern if THC were a highly toxic substance which remained physiologically active while stored in body fat. The evidence that THC is a highly toxic substance is weak, although it does have a bewildering variety of biological effects (Martin, 1986). Its degree of activity while stored has not been investigated. One potential health implication of THC storage is that the release of stored cannabinoids into blood may produce unexpected symptoms of cannabis intoxication. The release of stored THC has been suggested as an explanation of "flashback experiences" (e.g. Negrete, 1988; Thomas, 1993). Such experiences have been rarely reported by cannabis users (e.g. Edwards, 1983), and even in these cases interpretation of their significance is complicated by the fact that those who have reported such experiences have typically used other hallucinogenic drugs. Whatever the uncertainties about health implications of THC storage, all potential users of cannabis should be aware that it occurs.

9.2.2 Increases in the potency of cannabis

Cohen (1986) has been credited (Mikuriya and Aldrich, 1988) with initiating the recent claim that the existing medical literature on the health effects of cannabis underestimates its adverse effects because it was based upon research conducted on less potent forms of marijuana (O.5 per cent to 1.0 per cent THC) than those that became available in the USA in the past decade (3.5 per cent THC in 1985-1986). This claim has been repeated often in the popular and scientific media, and supported by anecdotal evidence that samples containing up to 40 per cent THC have been seized by the police. An alleged "ten-fold" increase in potency has contributed to recent concerns about the health effects of cannabis, because of the assumption that increases in average potency necessarily mean substantial increases in the health risks of cannabis use. In Australia this concern has been recently raised by the discovery of hydroponically cultivated clones of cannabis plants that produce high levels of THC, and by reports of the importation of high THC producing strains of cannabis from New Guinea.

There are a number of points to be made about this issue. First, the evidence for an increase in potency is not as clear as Cohen (1986) claimed, or as it seems from the data reported by ElSohy and ElSohy (1989). The inference that these data demonstrate that potency has increased depends upon the assumption that the samples analysed are representative of cannabis consumed. Mikuriya and Aldrich (1988), for example, have contested this assumption. They cite the results of chemical analyses conducted on cannabis samples in California during the middle 1970s in which the average potency was well within the ranges reported in samples seized by the US Drug Enforcement Agency in the middle 1980s. They also argue that the analyses of the DEA samples from the middle 1970s underestimated THC potency because the samples were not properly stored, allowing their average THC content to be degraded.

Second, even if we allow that there probably has been a small increase in the THC potency of cannabis products in the USA, there is at present no evidence of a similar increase in Australia. There is good evidence from police samples analysed in New Zealand over the past decade that average potency has not increased there (Bedford, 1993). Press reports of increased potency have often been misleading in that they have been based upon individual samples of highly concentrated cannabis extracts, such as hash oil, which have never had a major share of the cannabis market.

Third, the use of average potency can be also be potentially misleading, since the average ignores differences between cannabis users in preferences for cannabis products of varying potency. There probably has always been a market for more potent products among the heavier, and hence, more THC-tolerant, cannabis users. Marijuana probably remains the majority preference of cannabis users, although this is an issue worthy of investigation.

Fourth, it is not obvious that more potent forms of cannabis inevitably have more adverse effects on users' health than less potent forms. Indeed, it is conceivable that increased potency may have little or no adverse effect if users are able to titrate their dose to achieve the desired state of intoxication, as some have argued they do (e.g. Kleiman, 1992; Mikuyira and Aldrich, 1988). If users were able to titrate their dose, the use of more potent cannabis products would reduce the amount of cannabis material that was smoked, which would marginally reduce the risks of developing respiratory diseases.

Fifth, even if users do not titrate their dose of THC, (or if they do so inefficiently), any increase in the average dose received would not inevitably have an adverse impact on users' health. The effect would depend upon the type of health effect in question, and the relative experience of users. Higher average doses may produce an increase in the risk of minor adverse psychological effects of acute use, especially among naive users. This could be a desirable outcome if it discouraged further experimentation with the drug. Among experienced cannabis users, an increased average dose may increase the risks of accidents among those who drive while intoxicated, especially if combined with alcohol. Higher average doses may also increase the risk of regular users developing dependence.

All considered then, it is far from established that the average THC potency of cannabis products has substantially increased over recent decades. If potency has increased, it is even less certain that the average health risks of cannabis use have materially changed as a consequence, since users may titrate their dose to achieve the desired effects. Even if the users are inefficient in titrating their dose of THC, it is far from certain that the probability of adverse health effects will be thereby increased. Nevertheless, given these concerns about THC potency, it would be preferable to conduct research on the issue rather than to rely upon inferences about the likely effects of increased cannabis potency. Studies of the ability of experienced users to titrate their dose of THC would contribute to an evaluation of this issue, as would the inclusion in sample surveys of questions about the form and perceived potency of cannabis products used.