As Malta became the first country in Europe to legalise cannabis last week, and Luxembourg is set to follow in its heels, the debate and research into whether weed can damage mental health is set to intensify.

Ongoing research and scientific debate are also destined to influence the regulatory regime on cannabis, as well as social discourse – and attitudes – towards cannabis.

There has been intensified research by mental health academics in recent years, as well as much controversy over inconsistent findings.  

At the heart of the matter is the exact nature and extent of association between the psychoactive ingredient in cannabis, called THC, and the incidence of psychosis, particularly schizophrenia.

A major study by researchers from King’s College London and the Rivierduinen Institute for Mental Health Care in Holland has triggered controversy that has even spilled on the pages of the eminent journal The Lancet Psychiatry. The large-scale research project took place in major European cities, including Amsterdam and London, and reported a “causal link” between daily consumption of high-potency cannabis – defined as cannabis with over 10 percent THC – and psychotic disorders. 

It is worth noting that the potency of cannabis has been increasing by selective breeding, but Malta lags behind European cities in the trend towards increasing potency – more on this below.  

Rendition of psychosis. (Image copyright Camila Quintero Franco on Unsplash.)

That research drew the conclusion that “if high-potency cannabis were no longer accessible” the incidence of psychotic disorders in Amsterdam, and that triggered howls of dissent by some fellow scientists.   

These were articulated in an article by two Dutch academics – Iris E Sommer and Wim van den Brink – who wrote: “Our findings strongly suggested that associations between measures of cannabis use and psychosis or psychotic disorders are far more nuanced than Di Forti and colleagues assume.”

They made the point that cigarette smoke and nitrogen oxide (an air pollutant) are also linked to psychotic disorders, and hence any possible contribution of THC cannot be taken in isolation. They also quoted from another major study that drew a link between cannabis and schizophrenia in reverse: that it is latent or existent schizophrenia that predisposes individuals to heavy cannabis consumption, and hence heavy cannabis use is a manifestation of schizophrenia, not a precursor or trigger of it.

In a nuanced paper, Sommer and van den Brink also accepted that “high-potency cannabis use can lead to drug-induced psychosis and might trigger earlier onset of psychosis in genetically vulnerable individuals who would have developed psychosis anyway.”

They however qualified that by arguing that “previous studies indicate that frequent cigarette smoking and urban living each approximately double the risk of psychosis. Therefore, the question arises as to whether urban living, cannabis smoke, and tobacco smoke have a common factor that can cause psychosis. In summary, nitrogen oxide exposure—from all types of smoke—might be a more ubiquitous explanation for the reported link between cannabis and psychosis.”

Another scientist that waded into the debate, Suzanne H Cage, wrote that “it is perfectly possible that the association between cannabis and psychosis is bidirectional”, adding that a confluence of studies “indicate that for some individuals there is an increased risk of psychosis resulting from daily use of high potency cannabis.”

A crucial variable is the potency of cannabis. In Malta the prevalence of cannabis was traditionally low-potency hash imported from Morocco, but the supply has steadily shifted to higher-potency buds of weed imported from Sicily. A superintendent at the Drugs Squad told this website that around seventy percent of busts are of cannabis imported from Sicily.

Yet even most Sicilian bud is still less strong that varieties found in London – which goes by the street-name of ‘skunk’ – or Amsterdam, where selective breeding has increased THC levels of 20 percent or more.  

“Given the changing legal status of cannabis across the world,” Cage argued, “and the associated potential for an increase in use, the next priority is to identify which individuals are at risk from daily potent cannabis use, and to develop educational strategies and interventions to mitigate this.”

Sources in Maltese psychiatry have told this website that around one percent of the population in Malta may be affected or predisposed towards schizophrenia.

Yet in the noise surrounding the moves towards legalization in Malta, views have tended to become binary, and that makes it harder to discuss strategies on cannabis potency or use that would mitigate potential mental health effects.    

One strategy could be for the government to find ways to encourage – and for consumers to embrace – low potency cannabis, defined as less than 10% THC. A point worth remembering is that the predominant cannabis on the market in Malta has long been Moroccan resin with less than 4 percent THC, and it would not be reinventing anything to keep the THC percentages in the single digits – that still delivers a high, while reducing any potential effects on mental health.   

Another would be mode of intake: scientists for example recommend vaping over smoking.

Featured Picture: Cannabis bud. (Copyright Tim Foster on Unsplash.)