Legalizing recreational cannabis use: a promising journey into the unknown
Authors: Jan C. van Ours
Journal: World Psychiatry (2020)

There are many arguments in favor of legalization of recreational use of cannabis. Legalization removes incentives for criminal organizations to be involved, allows for quality control, raises tax revenues, and facilitates researchers to collect and analyze high-quality data. Hall and Lynskey1 provide an interesting overview of the public health consequences of legalizing recreational cannabis use. With this legalization, some US states have become frontrunners in international cannabis policy. Research-wise and policy-wise, there are two main issues, i.e. how legalization affects cannabis use and how cannabis use affects health. My reading of Hall and Lynskey’s paper is that there are quite a few uncertainties regarding both is­sues. From the research viewpoint, any study that aims to investigate determinants and consequences of cannabis use is hampered by the lack of a suitable experimental set-up. It is difficult to imagine research on legalization of cannabis use or cannabis use itself implemented through a randomized controlled trial. As far as I am aware, there is only one such study available2. This was conducted over a period of 98 days in Toronto, Canada, and aimed to explore the re­lationship between cannabis use and work­place behavior. Participants were recruited from volun­teers who had been using cannabis for about two years. During the experiment, par­ticipants could earn income by weaving sash belts on portable hand-looms. Workplace behavior was measured as daily production, daily working time and output per hour. Participants were randomly assigned to an experiment group or a control group. Those in the experiment group were required to smoke every day two cigarettes each containing 8 mg of tetrahydrocannabinol (THC). For them, cannabis use was legalized, as they were allowed to purchase a further unlimited number of cannabis cigarettes at a low price. Those in the control group were not required to smoke cannabis cigarettes. These cigarettes were available for them to buy, but had a substantially low­er THC content. Two main conclusions could be drawn from the experiment. First, legalization did not result in substantially higher levels of cannabis use. Second, large scheduled doses of cannabis had no adverse effects on any production measure. This study was limited due to the peculiar design and the brief duration of the experiment, and because the effects were measured in terms of workplace behavior rather than mental health. When it comes to mental health effects, a further complicating matter is the measurement issue, regarding both the outcomes to be measured and the assessment instruments to be used3. When considering the effects of legalizing recreational cannabis use, it is important to keep in mind that the initial decision to make cannabis illegal was not well motivated. Apparently, it was Egypt that put cannabis on the League of Nations’ international agenda. However, medical knowledge on the relationship between cannabis use and mental health problems at the time was based on presumptions rather than proof4. The main “evidence” seems to have been based on interviews with patients at a hospital for the insane. Anyway, in that study, prohibition of cannabis was deemed unwise because “its place would be taken by another euphoric agent, probably alcohol”, and alcohol was thought to be a “fertile cause” of insanity5. Unfortunately, this policy advice was ignored, and the 1925 International Opium Convention in Geneva decided that cannabis was as addictive and dangerous as opium. Liberalization of cannabis use may some­times be unintended. In 2017, low-THC cannabis was legalized in Italy as a by-product of a law that regulated the production and commercialization of hemp. Thus, the use of light cannabis (C-light) was unintentionally liberalized6. This apparently affected both the supply of illegal cannabis and the use of regular prescription drugs. With the legalization there was a reduction in confiscations of illegal cannabis, suggesting that criminal organizations suffered from the unintentional legalization6. The legalization of C-light also reduced the use of prescription medicines such as anxiolytics (–11.4%), antipsychotics (–4.8%), opioids (–1.2%) and antidepressants (–1.2%)7. So, self-medication through C-light apparently replaced in part the use of prescription medicines treating symptoms for which cannabidiol is considered to be effective. Interestingly, this substitution increased the costs for users, as regular prescription medicine is either fully reimbursed or subject to a small co-payment, whereas C-light is not cheap. Thus, cannabis has been declared illegal almost by coincidence, without an appropriate balancing of the pros and cons of doing so. Its illegal nature has made it difficult to explore its potential as a medicine. Indeed, “cannabis sits in an unusual medical no-man’s-land: neither licensed for most of the uses for which people want it, nor tested to the standards that patients usually expect from medicines”8. The good face of cannabis is that it in some cases it may be a substitute for prescription medicines; the bad face is that in other cases it may have negative mental health effects. The balancing between these effects has become impossible to make. Clearly, legalizing cannabis is going to have complex consequences for cannabis use and thus for public health. However, legalization also provides opportunities to better understand how cannabis may be beneficial for mental health. Indeed, as Hall and Lynskey argue, the legalization of recreational cannabis use in Canada, Uruguay and various US states “is a large scale policy experiment whose effects may not be known for a decade or more”1. The experiment is there because ex ante its net effects were expected to be positive. I am inclined to think that also ex post the experiment will turn out to be successful.