• Cannabis;
  • combined use;
  • drug policy;
  • marijuana;
  • outcomes;
  • tobacco

Peters et al. found [1] in their literature review that the combined use of cannabis and tobacco worsened outcomes for cannabis but not tobacco, compared to the use of one of these drugs. This conclusion is hardly surprising. While the implications for clinical practice and research are small, the policy implications are of considerable interest, especially when seen in the larger perspective of cannabis being an illegal drug while tobacco has always remained legal (in the contemporary era).

Half of all cigarette smokers die from a tobacco-related illness. In contrast, the contribution of cannabis to physical illness is modest and dwarfed by tobacco. While debate continues regarding the nature and extent of mental illness confidently attributable to cannabis, evidence of at least some risk of mental illness appears to be increasing. The precautionary principle suggests that the benefit of any doubt should be given at this stage to presuming the existence of significant cannabis-related mental illness. Nevertheless, the burden of disease is estimated to be almost 40 times greater for tobacco (7.8%) than cannabis (0.2%) [2] in Australia, a country with a relatively low prevalence of cigarette smoking and a very high prevalence of cannabis smoking.

The prevalence of smoking cigarettes has dropped sharply in countries where governments have been prepared to implement evidence-based policies, usually against ferocious tobacco industry opposition. In contrast, the global prohibition of cannabis, now almost 90 years old, is supported by little evidence of effectiveness—although ample evidence often exists of serious unintended negative consequences. The prevalence of cannabis consumption in most countries fluctuates somewhat, in contrast to the striking decrease in the prevalence of tobacco smoking now seen in many countries. Prohibition has not succeeded in making cannabis difficult to obtain. In the United States, more than 80% of 12th-grade high school seniors reported in annual surveys between 1975 and 2011 that cannabis was ‘fairly’ or ‘very easy’ to obtain [3]. Meanwhile, support in the United States for the legalization of marijuana has increased [4] from 12% in 1969 to 50% in 2011, while opposition dropped from 84% in 1969 to 46% in 2011. Supporters now outnumber opponents, while the change in opinion appears to have accelerated in recent years.

The study by Peters et al. [1] was funded by the National Institute of Drug Abuse (NIDA), an agency of the US government responsible for funding 80% of the illicit drugs research in the world. NIDA is hardly a scientifically impartial agency. A NIDA spokeswoman (Ms Shirley Simson) said in 2010: ‘as the National Institute on Drug Abuse, our focus is primarily on the negative consequences of marijuana use. We generally do not fund research focused on the potential beneficial medical effects of marijuana’[5]. In contrast, US federal and state government policy on tobacco is often tepid. The mean state tax in 2011 on a 20-cigarette pack in the United States was $1.46 [6]. However, in the six major tobacco-growing states the mean state cigarette excise tax was only $0.49 cents per pack in 2011.

Why is this discussion of the broader context relevant? Given the major finding of this study it would be logical for the authors to warn, through readers of this journal, the potential users of both these drugs and policy makers, that cannabis smokers who also smoke tobacco risk exacerbating cannabis-related problems. Clearly, the harm reduction implication is that cannabis users should be warned to avoid mixing their preferred drug with tobacco. However, Peters et al. [1] remain silent about the harm reduction policy implications of their study, preferring to comment only on the safer clinical and research implications.

The arbitrary historical basis of global cannabis prohibition is rarely noted. The critical decision to ban cannabis internationally was taken at a 1924–25 League of Nations meeting in Geneva. A review of the meeting [7] noted that: ‘although cannabis (Indian hemp) was not on the agenda of the Second Opium Conference, a claim by the Egyptian delegation that it was as dangerous as opium, and should therefore be subject to the same international controls, was supported by several other countries. No formal evidence was produced and conference delegates had not been briefed about cannabis’. It is hardly surprising that the mighty edifice of global cannabis prohibition, built on such rickety foundations, is now beginning to totter. At least there is some consistency from the 1925 claim that cannabis is as dangerous as opium to a 2012 comment which avoids making the obvious recommendation that cannabis smokers should be warned against combining cannabis with tobacco. T. S. Eliot could have been commenting on drug policy when he observed that ‘humankind cannot bear very much reality’.


  1. Top of page
  2. Declaration of interests
  3. References