In the last week, two scientific papers have made a renewed case against cannabis based on the potential risks to users’ mental health. Rather than dismissing them as more prohibition propaganda, Cannabiz editor-at-large Rhys Cohen analyses the evidence and what it means for industry advocates.

When a scientific paper is published that even hints at the possibility of cannabis having medicinal or socially beneficial effects, people in the industry (such as myself) are quick to celebrate. A lot of the time, the technical content of these publications goes over our heads. I, for one, am not a scientist. But we are happy to take the scientists at their word.

Cannabiz editor-at-large Rhys Cohen

When a paper concludes that some kinds of cannabis use may be risky or harmful, we tend to dismiss it. Our impulse is to disbelieve the findings because they conflict with our established beliefs. You can’t blame pro-cannabis people for being sceptical – we’re only now emerging from decades of literal propaganda, deliberately orchestrated by the most powerful institutions in the world. There’s that old saying: just because you’re paranoid, doesn’t mean they’re not out to get you.

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But we should resist this impulse for two reasons. First, if you care about broader drug law reform, you need to understand what people’s concerns are, and be able to engage with them in an informed way. And second, they might be right. Just because the risk of schizophrenia and mental illness have been cynically used to attack cannabis, that doesn’t mean those risks are entirely fictitious. The good news is, taking these concerns seriously actually supports the case for cannabis legalisation.

In the last week, two scientific papers caught my attention, both about the potential risks of cannabis use to mental health. The first was this paper, published in JAMA Psychiatry (that’s a very prestigious journal). It is an analysis of every person living in Denmark who was 16 years or older between 1972 and 2016. That’s more than seven million people. The study looked at the relationship between cannabis use and the development of schizophrenia.

It found that, over the last 20 years, the proportion of people in Denmark with schizophrenia associated with cannabis use increased three to four-fold. And the proportion of the population with schizophrenia also increased over that time. So, more Danes with schizophrenia overall, and a growing number of those with schizophrenia associated with cannabis use. This doesn’t prove that cannabis causes schizophrenia, but it’s a massive study and a reputable data set, so the correlation cannot be ignored.

The second paper was published in Drug and Alcohol Review (a much smaller, but still reputable drug policy journal). It analysed data taken from the Australian National Drug Strategy Household Survey (NDSHS). This is the same survey I wrote about last year, that had some interesting findings about medical cannabis specifically.

The paper conducted some in-depth statistical analysis of one of the questions in the NDSHS, which asked people if they would start using cannabis, or increase their cannabis use, if cannabis was legal and available. The paper found that about 7% of Australians aged 14 and older who have never used cannabis would try it, and about 18% of people who have used cannabis at least once in their life would increase their cannabis use, if it were legal and available. Both of those figures have increased significantly and steadily since 2013.

Worryingly, the more psychological distress people reported living with, the more likely they were to say they would try cannabis for the first time. Younger people living with psychological distress were also more likely than older people to say they would try cannabis, if it were legal and available. The same trend was also identified in people who had already used cannabis at least once in their life, reporting that they would use more cannabis if legal and available.

So, some pretty dire findings, right? I’m sure plenty of people read those papers and thought “better keep it prohibited then”. That’s certainly what the authors of the second paper concluded. But that would be a scientifically lazy, if not outright dishonest, conclusion to reach. Here’s why…

First, the Denmark paper. The authors suggest that increasing rates of cannabis use, combined with increasing cannabis potency, could be to blame for increasing rates of schizophrenia associated with cannabis use. That may or may not be true. But let’s assume it is. What does it tell us? Denmark prohibits cannabis for non-medical purposes and has done so for decades. Since the 1990s, rates of cannabis use, rates of cannabis-associated schizophrenia, and the potency of cannabis have all increased. If these are causally linked, it is the best evidence yet that prohibition has failed. The only reasonable response to this trend is to regulate the cannabis market to reduce these risks to public health.

Now to the second paper. I know I prefaced this whole article by saying that, if we’re prepared to take scientists at their word when they find something positive, it would be hypocritical to not do the same with negative findings. But that doesn’t mean we have to swallow everything hook, line and sinker. Even us non-scientists can – and should – point out errors when we see them in scientific papers.

So, first of all, the findings of this paper are based entirely on a single question from the NDSHS. And that question asks people what they would do if cannabis was ‘legal and available’. To me, that means if cannabis was legalised. Like, you could walk into a store and buy some. And there is a big difference between ‘legalised’ and ‘decriminalised’.

There is a big difference between ‘legalised’ and ‘decriminalised’ cannabis use

Decriminalisation, for those who aren’t aware, is the removal of criminal penalties. Changing the law so that, instead of going to prison for cannabis possession, you get a fine instead. Or you get sent to mandatory drug and alcohol treatment. In most places in Australia, cannabis is already decriminalised to some extent. That’s why about half of all people in New South Wales caught with small amounts of cannabis never end up in court. Most offenders get off with a warning. Unless you’re aboriginal, in which case it’s vastly more likely that the police will choose to drag you into court. And decriminalisation, by the way, has been consistently found to be a better policy approach than having severe penalties. For a whole number of very obvious reasons.

So, you can imagine my surprise when the paper we’re talking about not only failed to distinguish between ‘legalisation’ and ‘decriminalisation’. But actually used the NDSHS data, which asked about cannabis being ‘legal and available’, to argue that these findings relate to cannabis decriminalisation. And, worse still, this paper goes on to argue that any attempt to decriminalise cannabis would have a number of negative consequences, including increasing demand for residential drug rehabilitation for young people, which…

“…could not be described as inexpensive. The current findings thus underscore the point that there are costs associated with cannabis use decriminalisation, just as there are costs associated with cannabis use prohibition.”

What a load of rubbish.

“Prohibition continues to fail. We must move to a regulated market for adult-use cannabis.”