Cannabis legalisation: what does the emerging evidence say?

by Katya Kowalski

Lots of arguments get thrown around when it comes to recreational cannabis legalisation, with claims that usage goes down and mental health outcomes improve. But, what does the literature say currently?

With US states continuing to legalise and more European countries joining in on recreational reform, it is worth examining the current bank of evidence. We need to understand what we may still have to consider when it comes to policy implementation.

I would like to start this piece with two caveats. 

  1. This article is by no means a systematic review of the current literature around the impacts of cannabis legalisation. This piece includes the recent studies I have come across in my reading and research on the topic, which I think are interesting and worth discussing.
  2. I support sensible recreational cannabis reform. I hope that this article highlights that there are shortfalls and considerations for cannabis reform that need to be taken into account. One can be supportive of reform, whilst aware that legalisation isn’t a silver bullet.

The studies I’ve selected highlight some of the most common concerns and arguments when it comes to the legalisation of cannabis. So, let’s dive in.

Mental Health Outcomes

The link between mental health problems and cannabis use has got to be one of the largest arguments against reform – let’s take a look at emerging data on this.

A study published in June 2023 found that where US States have adopted recreational cannabis policies, admissions for mental health treatment have dropped, going against some of the key arguments against legalisation. It is important to note that findings across the board for this outcome do still vary, with a mixed consensus around the effects of legalisation on mental health. So, it’s not quite that straightforward (nothing with cannabis ever is).

It should also be considered that just because there are lower admissions, does not mean that a jurisdiction actually has better mental health. This isn’t a causal link and it is possible that with cannabis legalisation fewer individuals are seeking professional help, instead are self-medicating to ease their symptoms. This may deter some individuals away from seeking help. This is speculative though – on the surface mental health admissions don’t appear to worsen as a result of legalisation.


Though not linked directly to legalisation, I think it’s worth touching on potency as that gets mixed into the mental health debate a lot. A study released in 2023 examined the association between cannabis potency and mental health outcomes. The study failed to identify an association between more potent cannabis and increased use of dependence, depression and psychosis. Though these results are not conclusive, it would suggest that increased cannabis potency may not have as large of an effect on dependence as was thought. This research is important for when we speak about the potency of cannabis increasing with legalisation. Though this is true, potency may not have as much of an effect on mental health outcomes as we think.

Of course, research does show that people who are at a clinical risk of psychosis, are more likely to develop psychotic disorders from cannabis use. So those with a clinical vulnerability are prone to developing a problematic relationship with cannabis. This isn’t necessarily a byproduct of legalisation but increased availability can lead to individuals using cannabis when they shouldn’t.


One of the biggest fallacies with cannabis legalisation is the assumption that use amongst the population will go down. Obviously usage will increase –  the main reason a big chunk of the population don’t use cannabis is because it is illegal, once that changes the cohort of people using the drug changes. 

However, it’s important to distinguish use and problematic use. A study published this year looking at the trends in Canada found that there was no change in the proportion of “high risk individuals” using cannabis as a result of legalisation. This is good news!

Another study from 2023 reviewed literature on the relationship between availability of legal cannabis with behavioural outcomes in North America. The results demonstrated that the groups that are least exposed to cannabis before legalisation may be the most susceptible to its increased availability. This is the point I made above, usage and interest in cannabis is certainly going to increase with legalisation. This isn’t necessarily a bad thing, it just has to be monitored to ensure that use isn’t problematic. 

Though the link between availability and risky use is less clear with legalisation. So, restrictions on where and how cannabis is sold, appears to be warranted. This is supported by research conducted in 2020, which also finds an increase in use.

Cannabis use amongst young adults is consistently an area for concern with cannabis. A cross-sectional study collected data through surveys on self-reported cannabis use in the past month, to examine youth use trends after legalisation in the US. Results showed that prevalence increased after cannabis legalisation, including cannabis use disorder. 

The main takeaway from this is that young adults are sensitive to recreational legalisation and as a result there should be appropriate prevention efforts to deter use amongst under 21 year olds.


Among the jurisdictions that have legalised cannabis, they all are yet to perfect it. The evidence outlined in this article provides some insight into the outcomes associated with cannabis legalisation so far. Is it perfect? No. But it is a hell of a lot better legalising it than leaving it inn the hands of organised crime. 

As highlighted in Professor Armstrong’s work, it is vital that jurisdictions which legalise cannabis, collect data relevant to cannabis so that these effects can be examined. With legalisation coming to Europe, there should be consideration amongst governments to allocate funding to monitor impacts and minimise any adverse effects from cannabis legalisation.

Overall, the evidence in jurisdictions that have legalised looks promising – mental health outcomes remain intact, potency does not appear to have a significant effect and although usage goes up, problematic use does not necessarily increase.

This piece was written by Katya Kowalski, Head of Operations at Volteface. Tweets @KowalskiKatya

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