The potential health risks associated with using illicit drugs remain the key argument for maintaining their criminal status. And although many studies find that drug users are in worse health than nonusers, the proper interpretation of this evidence is contentious. This is because, in order to conclude that it is in fact their drug use that causes them poor health, two alternative explanations for the association must be eliminated. This issue is not new. Determining the true nature of the relationship between drug use and health has a long history. An early example of a discussion of the issues can be found in the 1894 Indian Hemp Commission Report (Kendell, 2003). The first alternative explanation is referred to as reverse causality. Under reverse causality, the observed relationship between drug use and poor health runs in the reverse direction – from poor health to drug use. This may occur if, for example, people use illegal drugs to treat symptoms of their illness. The second alternative explanation is referred to as spurious correlation. This is an issue if there exists an unobserved factor, for example, childhood abuse, which causes both drug use and poor health. If this is the case, then the resulting correlation between drug use and poor health is spurious because drug use is simply capturing the unmeasured effect of the confounding factor, childhood abuse, on health. Untangling these competing and more than likely coexisting mechanisms generating the observed relationship between drug use and health is not merely of academic importance. The economic cost of maintaining criminal sanctions for illicit drug use is large. This cost is typically justified on the grounds that criminalizing drug use prevents health-related harms associated with drug use. For this reason, it is important to know whether and to what extent drug use causes ill health. This article reviews the evidence on this issue.
To begin, section The Extent of Illegal Drug Use introduces facts and figures regarding the extent of illicit drug use. To do so, the authors present data on the prevalence and intensity of use for the major illicit drugs: heroin, cocaine, amphetamines, ecstasy, and cannabis. These data illustrate the dominance of cannabis among illegal drugs. Although the prevalence of drug use provides an overview of the extent of drug use in a population, it is not necessarily informative about the type of drug use that may give rise to health-related problems. For example, the prevalence of use is unable to distinguish between those who have experimented once or twice (in the given time frame) and the more policy-relevant group who become long-term heavy users. Second, there is mounting evidence that uptake of drugs in the teenage years carries significantly more risks than uptake at later ages. Therefore, it is not simply the prevalence of use, but the age of first use and the duration of use that is informative in terms of risk of potential health-related harms. To provide information on these dimensions, the authors describe the dynamics of drug use. They do so for cannabis as this is by far the most popular illegal drug.
In Section Health Effects of Illegal Drug Use, the authors present and discuss a number of recent studies on the direct and indirect health effects of cannabis use. They distinguish between epidemiological and econometric studies. Section Discussion and Conclusion concludes that although consumers of illegal drugs are assumed to face substantial health risks, the evidence base regarding the nature and extent of these risks is, by and large, yet to be well established. For the most popular illegal drug, cannabis, there do not seem to be serious harmful effects with moderate use. There may be negative harmful effects for heavy users who are susceptible to mental health problems.