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Research & Development Adverse effects, Neurology & psychology

Cannabis on the Brain

Claims of adverse effects from cannabis range from cardiovascular disorders to abnormal brain development. But perhaps the most frequently discussed health impacts are those affecting mental health – and a recent study adds compelling new evidence (1).

The aim of the case–control study was to investigate the link between cannabis use and incidence of psychotic disorders. The researchers focused on patients presenting with their first psychotic episode across several sites in Europe and Brazil, and used logistic regression models based on Europe-wide and national data on the expected concentration of THC in different types of cannabis to uncover the potential associations. “A higher incidence of daily cannabis use and more frequent use of high-potency types led to a greater number of new cases of psychosis per person-year,” says lead author Marta Di Forti. The findings, she says, tally with her own clinical experience as a psychiatrist in London, where high-potency cannabis is widely available.

When using high-potency cannabis, the study demonstrated a risk of psychotic disorders approximately five times higher for daily users compared with those who never use the drug. When not considering cannabis strength, the risk was approximately three times greater for daily users. The team estimate that roughly 30 percent of cases of first-episode psychosis in London and 50 percent in Amsterdam could be prevented, if high-potency cannabis was no longer available.

Asked about the significance of high- versus low-potency strains, Di Forti drew an analogy to alcohol: “It is like the difference between beer and vodka in terms of liver damage. More potent cannabis has more THC, the cannabinoid associated with psychotic symptoms.” Continuing the comparison, Di Forti believes that the results will be applicable to any culture in which cannabis is accessible, just as the health impacts associated with alcohol use are apparent wherever alcohol is found.

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  1. M Di Forti et al., “The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study,” Lancet Psychiatry, 6, 427-436 (2019). DOI: 10.1016/S2215-0366(19)30048-3
About the Author
Matthew Hallam

I've always wanted a career in which I could practice my creativity, even when I worked on the assembly line in a fish factory. At one time, I channeled this need into dance, drawing, poetry and fiction, and I still do most of these things. But, following completion of my MSc(Res) in Translational Oncology and time working in labs and as a Medical Writer for major pharmaceutical companies, I'm happy to find myself in a career that allows me to combine my creative side with my scientific mind as the Deputy Editor of The Analytical Scientist.

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