Analysing the Evidence for Cannabis Legalisation

by Oliver Callaghan

Prior to the legalisation of cannabis, many of the same talking points were used to produce fear around policy change. Whether these arguments were based on cultural, behavioural, or psychological concerns, over a decade later one would expect any of the concerns around cannabis legalisation to be visible in jurisdictions that have gone through with reform. This article will examine the data behind a variety of assertions to determine whether cannabis legalisation has played out as expected.

Evidence for youth cannabis use post legalisation

A common assertion which circulated in the anti-cannabis debate was the notion that cannabis legalisation would increase access for those under-18. Proponents of this argument stated that increased access would encourage use by younger users, which could cause a range of unanticipated psychological and social issues in the future.  

By comparing data from the SAMHSA National Survey on Drug Use and Health from 2002 to 2022 (page 17), we can see that the percentage of cannabis consumption under the age of 18 has decreased significantly. In 2022, 6.4% of 12-17 year olds stated they used cannabis in the last month compared to 6.5% in 2016 (page 170), 7.4% in 2010 and 8.2% in 2002. 

These statistics suggest that the legal status of a drug simply does not contribute to the use rate among children and adolescents. Although there is only a 1.8% reduction in the usage rate over 20 years, this trend is particularly significant when considering the normalisation of cannabis in the USA during this time. To put this into perspective, other demographics such as 18-25 year olds have seen an increase in usage from 17.3% in 2002 to 25.9% in 2022. Data from the national survey suggests that cannabis use is now exceeding the use of alcohol, yet cannabis use among children and adolescents remains comparatively low.

While there is still a lot to learn on the effects of cannabis on developing minds which should be investigated, the assertion that liberal cannabis laws increase usage among children was misleading, especially when the data demonstrates that legalisation could have contributed to lower use among under 18s. At the moment it is far easier for under-18s to access cannabis illegally because dealers don’t check IDs – bringing it into a legal framework changes this. 

On the other hand, the impact of alcohol on the developing mind is well documented. Underage drinking can affect academic performance, stunt the formation of the prefrontal cortex, influence antisocial behaviour, and permanently alter young people’s regulation of memory and emotions. In the same 2022 SAMHSA survey, 6.8% of 12-17 year olds stated they used alcohol in the past month. 

This suggests that problematic underage exposure to substances could rest more on how we are equipped to educate and support at-risk socio-economic cohorts of young people, rather than the availability or legality of these substances. 

What effect does cannabis legalisation have on psychosis?

This might be the most contentious topic to provide answers for. While there have been a number of articles and studies on the sharp increase in hospitalisations for psychosis following cannabis legalisation, the data on this topic is often ambiguous and complex

An article by Psychiatric Times highlighted the association between schizophrenia and cannabis use disorder, arguing that one in four schizophrenia patients were found to have a cannabis use disorder. While this suggests that cannabis legalisation could increase consumption among those with a genetic predisposition to schizophrenia, the picture is not as clear as it may seem. 

Many of the studies on this topic rely on self reporting, and can vary widely depending on the frequency of use, THC content, and the method of consumption (resin, flower, edibles etc). While there is some evidence that daily cannabis use is linked to temporary psychosis and schizophrenia, these appear to be linked with those with those with genetic predispositions of neuregulin 1 (NRG1), catechol-O-methyltransferase (COMT), and the AKT1 gene which interact with THC.

Studies which have examined the association between cannabis legalisation in the US and Canada found no statistical significance in the rates of schizophrenia or antipsychotic prescriptions. Although it is important to study this topic in more depth to minimise the risk of psychiatric disorders, there is a fine line between informing the public and instigating moral panics which must be navigated rationally.

Furthermore, although psychosis is a risk factor for some of those who consume cannabis, the harms pale in comparison to the lethality of other drugs such as opioids and alcohol. Opioid overdoses killed an estimated 107,543 people in 2023 according to the CDC. The CDC also estimates that alcohol killed around 178,000 people in 2020-21.

When these statistics are considered, minimising access to cannabis due to a subset of vulnerable outliers appears illogical. Furthermore, there is an argument to be made that those suffering with addiction could improve their health outcomes when considering the emerging research on medicinal cannabis as a substitute for opioids.

Does cannabis legalisation impact rates of driving under the influence?

Another important debate on the legalisation of cannabis relates to how legalisation impacts the rates of cannabis impaired driving and traffic fatalities. A report on the prevalence of cannabis impaired driving in Canada found that the rate of those who admitted to driving within two hours of cannabis use marginally decreased by from 14.2% to 13.2% after recreational cannabis was legalised in 2018. While the report also quotes data which found a higher proportion of drivers testing positive for cannabis (7.6%) than alcohol (4.4%) in random roadside tests between 2016 and 2018, it is difficult to evaluate how much cannabis legalisation influenced these statistics.

The main issue relating to this topic is the public perception of risk. While there are a number of massively funded public campaigns on the impact of drunk driving internationally, many young people do not believe that cannabis use impairs their driving and that it is harder to detect the signs of impairment when consuming cannabis. This highlights the importance of education which should accompany legalisation so that the assumption that legal substances are harmless can be dispelled. 

Similarly to the research on cannabis and psychosis, there are a number of variables which often muddy the water of data on this topic. There is data indicating that cannabis can impair psychomotor function, cognitive ability and reaction times. However, reports which refer to the percentage of road accident samples containing cannabis may not always be reliable due to the influence of polydrug consumption which are typically found in these samples. 

This makes it difficult to establish a causal relationship between the two factors, particularly when meta analyses on the topic have found inconsistencies between the quality of studies, publication bias, and an overestimation of the impact of impaired driving by less methodologically robust studies. 

In general, there appears to be a lack of consensus on how much of a factor legalisation has on driving under the influence of cannabis. However, it does appear as though the public’s perception of cannabis as harmless regarding driving indicates that more funding should be put into educating the demographics (typically young males) who are most often tested positive. 

Looking Ahead

In summary, the data in this article provides us with a number of insights about the legalisation of cannabis. While some of these claims are objectively false, there are also more controversial issues which need to be explored further.

Public information should be clear about the risk of driving under the influence of cannabis. Those who consume cannabis should also be informed about the genetic predispositions which could expose them to psychosis or schizophrenia if they heavily consume cannabis. There is a way of reducing the harm of these issues without catastrophising the impact of legalisation as a whole. 

While it is easy to get dragged into the weeds on this topic, it is important to zoom out a little. Cannabis legalisation has been a momentous victory for criminal justice reform in the USA. This movement has also spurred other countries to adopt pragmatic drug policy positions which have reduced harm, mitigated black markets and generated billions in tax revenue.

You may also like

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept

Privacy & Cookies Policy