To legalize or not to legalize cannabis, that is the question!
Authors: Marta Di Forti
Journal: World Psychiatry (2020)

The wave of changes in cannabis laws coming from the US and more recently Canada has pushed many countries, including the land of Shakespeare, into the dilemma of legalizing or not legalizing cannabis use. In the UK, a first step took place in November 2019, when medicinal cannabis became legal. Now British specialist physicians can prescribe cannabis for a handful of medical conditions. However, has the American experiment yet convinced its more cautious British allies to go all the way and legalize cannabis for recreational use? As a clinician and an academic living in UK and working on the link between cannabis use and psychotic disorder, I have been watching the American experiment very closely. Hall and Lynskey1 highlight that two of the key arguments of the legalization lobby are: a) that it will reduce adolescent access, and b) that the available cannabis will be ­safer and less potent because of state-con­trolled levels of its active ingredient, tetra­hydrocannabinol (THC). These are clever­ly chosen predictions to reassure both con­cerned parents and mental health professionals against the well-established association between cannabis use – especially when started in adolescence2 and of high potency types3 – and the risk to develop a psychotic disorder. But, have these two predictions held up against the evidence of time? Hall and Lynskey give a comprehensive snapshot of the outcomes that have followed the changes in cannabis law since 2012 in the US. So, what about adolescents use? The authors report that, while rates of cannabis use have increased among adults in states that have legalized cannabis, they have not changed among adolescents. Not surprisingly, as Canada, Uruguay and the US have legalized cannabis for adult use, whereas use remains illegal for adolescents, the latter continue to buy it from criminal gangs and they risk criminal prosecution for using it. Moreover, experience with both tobacco and alcohol has shown that adolescents’ choices are not influenced as much as adults’ by the legal status of a recreational drug. Furthermore, it is still early days to see whether the increase in rates of cannabis use among adults leaks down to influence younger groups. Indeed, data from a large and nationally representative US survey4 quoted by the authors, based on state-level estimates spanning 2008-2016, tentatively suggest trends of increase in cannabis use among young adolescents (12-17 years old) in those states where recreational cannabis use is legal. Similarly, in December 2019, the US Substance Abuse and Mental Health Administration (SAMHSA) released the data from their 2017-18 National Survey on Drug Use and Health. This showed that, in states where recreational cannabis is legal, past-month youth use is 40% higher, past-year youth use is almost 30% higher, and first-time youth use 30% higher compared to states where cannabis use is still illegal5. These data are quoted by Smart Approaches to Marijuana (SAM), the influential American anti-cannabis legalization campaign group6. SAM further remarks, with great concern, that past-month youth (aged 12-17) use continues on an upward trend in states with commercial sales. For instance, in Washington, where cannabis use is legal, over the past year there has been the largest surge in past-month youth use, with an 11% increase compared to a 4% increase in Colorado. What about cannabis potency where recreational use is legal? There is no doubt that, despite the declared intention, the potency of the types of cannabis legally available has gone up. Potent edible types are often available, and their price has gone down. For example, in Washington, where past-month youth use is going up, cannabis potency is spiralling up, reaching THC content equal to 70% or more7. Hall and Lynskey rightly point out that the reported widespread increase in types of cannabis with high levels of THC available at low prices exposes cannabis users to an increased risk to develop both cannabis use disorders8 and psychotic disorders. While only a minority of cannabis users develop a psychotic disorder, my colleagues and I have shown that users who consume daily types of cannabis with THC ≥10% are over 5 times more likely to suffer from a psychotic disorder than never users. Furthermore, we measured across 11 European cities how high availability of potent types of cannabis (THC ≥10%) impacts, at a population level, on rates of psychotic disorder. We found that in Amsterdam, where types of cannabis with an average THC of 29%, like Nederhasj, are commonly sold in coffee shops, up to 50% of new cases of psychotic disorder can be attributed to the use of high-potency cannabis. These data suggest that 50% of the new cases of psychosis in Amsterdam could have been prevented if these individuals had not added to their cluster of risk factors the use of high-potency cannabis, the most preventable among them. Indeed, in our study, the three cities with the highest incidence rates of psychotic disorder – London, Amsterdam and Paris – also had the highest rates of use of high-potency cannabis in the control samples representing their general populations9. So, while it is early days to measure the impact on rates of psychotic disorder of the increase in THC in the cannabis sold where recreational use is legal, it is an ­evidence-based prediction that the reported greater availability of high-potency cannabis will result in more people presenting with psychotic disorders associated with their cannabis use. Therefore, while we cannot stop the commercial force driving the cannabis business interests, we can learn how to act from our colleagues that have cautioned against the harmful effects of alcohol and tobacco. None of the countries that have legalized recreational cannabis, nor those which are considering to follow, have invested sufficient resources in education campaigns to engage the general public and especially young people in learning about the effects of cannabis on their developing brain, on their educational achievements, and on their risk to become dependent. There has been no attempt to use modern technology to test their knowledge on the topic and provide them with data. As the famous American jazz trumpet­er and cannabis user Miles Davis said, “knowledge is freedom and ignorance is slavery”. Therefore, the freedom that comes from legal access to cannabis might be on­ly an illusion if it is not accompanied by knowledge of its harmful effects. Rather than dwelling on “to legalize or not to legalize”, we should move on to ask for more education. We need public education to enable individuals to make an informed choice about whether and how to use cannabis, and to counter the influence of commercial pressures at a time where, for instance, in Colorado there are now more cannabis shops than Starbucks and McDonald's10.