Last week, NORML issued a blistering response to the wide circulation of a study published in The Lancet Journal of Psychiatry on March 19th, 2019. The study, lead by Dr. Marta Di Forti and produced by Kings’s College (London), concluded that daily use of high THC cannabis (14 - 15% THC) causes psychosis. The study’s findings were rebutted by NORML (National Organization for the Reform of Marijuana Laws), who decried the Lancet article as “premature at best, and sensational at worst” for claiming a “relationship exists between marijuana use and psychiatric disorders”.

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The National Alliance on Mental Illness (NAMI) describes Psychosis as “disruptions to a person’s thoughts and perceptions that make it difficult for them to recognize what is real and what isn’t.” NAMI further labels the Psychosis as “confusing” and “frightening.” 

Limited Data Means More Research Is Needed

Fresh agricultural hemp grows in the countryside iStock / JohnAlexandr

Studies have indeed shown some relationship between cannabis and psychosis. NORML admits as much in a less bully-like publication, which directly states “there is limited data suggesting an association, albiet a minor one.” To say there is no relationship is wrong. There is a general consensus that psychosis can result from heavy usage of cannabis. Unsurprisingly, this finding is common to abuse of other substances, including alcohol, hallucinogens, and sedatives. Cannabis also seems to activate users’ latent predisposition toward psychosis. This sensitivity toward exhibiting psychosis is thought to be a function of environmental and/or genetic factors, above the direct influence of cannabis. Not all users with category-appropriate genetic and environmental factors actually experience psychosis when ingesting cannabis. Adolescents are particularly susceptible to the onset of psychosis induced by cannabis when they have those environmental and genetic factors. As is clear here and in other publications amassing known studies, there is a great deal of good research, however, the scientific community has not definitively concluded an understanding of the linkage on the link between psychosis and cannabis.

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Cannabis research has been exploding in the United States since 2017. The truth is that we still don’t know what we don’t know about the complex interface between the body and the hundreds of chemicals and cannabinoids within the plant. Supporting or opposing the use of cannabis, at this point, becomes a question of seeing a glass as half-full or half-empty. Due to the changing landscape of what science tells us about cannabis, what appears to be a fortress today becomes an anthill tomorrow.

Breaking Down Dr. Di Forti's Study

Using marijuana cigarette in health purpose iStock / Biserka Stojanovic

Regarding the Di Forti study: an interesting finding (“also highly questionable”, according to NORML) is that the incidence of psychosis varies with THC content. This consideration deserves a follow-up, due to the limitations of the initial study, but also due to the pressing relevance for the modern American market. There is a clear societal trend toward buying super-boosting THC strains. Di Forti, in her studies, considers “High THC” as “10-15% THC.” That’s laughable because strains in the 30% are commonplace, with 10-15% THC strains being average.

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Unfortunately, Di Forti gathered inferior data, and so this study’s findings cannot be accepted. The study’s methodology cross-referenced subjects’ self-reported “type of cannabis” with Europe-wide data on the average THC found in cannabis in the subject’s country. Rather than enumerate the many problems with this approach, any cannabis user can spot Di Forti's fundamental naivety and failure to employ logic in her 2018 interview with Rethink Mental Illness regarding this data:

“Participants gave very clear and detailed reporting about the type of cannabis they used, as the different types can be distinguished by smell, taste and of course their recreational effects. This was not unusual - many of us who have tried alcohol could distinguish a glass of whiskey from a glass of beer, even with our eyes closed.”

What are the types of cannabis? Did the study collect data on sativa vs. indica, the popular standard that does not reflect inter-species chemical variance and cannabinoid diversity? Di Forti’s self-reported data is garbage and not reliable, but it might still be correct based on the large number of subjects and the relatively good national data on average THC levels in countries individual markets.

Reading through this interview gives the impression that Di Forti is interested in good science but adopts the difficult position of an obstructionist, sticking stubbornly to fear-mongering in the absence of conclusive (and truly needed) evidence on either side.

As stated by NORML, The Lancet Di Forti study goes too far claiming “causality” between cannabis and psychosis. As demonstrated above, good studies have been providing data suggesting a complex, multi-directional link between psychosis and cannabis for a decade. Recently, studies like those from McGuire (‘18) and Boggs (‘18) have even shown the potential for Cannabidiol (CBD) to treat mental health disorders, including Schizophrenia. Until Federal regulation allows for public money to support the study of cannabinoids, many of the USA’s top experts, sequestered in top Academic Institutions, are barred from the robust laboratory study everyone can agree is needed.