Is cannabis use really linked to psychosis? Scientists dispute findings

Image by Gerd Altmann from Pixabay

Seemingly contradicting the idea that cannabis and cannabis-derived products may have beneficial health effects, there are a few reports saying that regular cannabis use is directly linked to the development of psychosis. These results have been published in scientific journals over the years, contributing to the generalized fear and apprehension surrounding cannabis use.

One example of this is an article published in the prestigious scientific journal The Lancet Psychiatry earlier this year.

According to Marta Di Forti and her colleagues, the researchers that performed the study on European and Brazilian psychiatric patients, the daily use of high-potency types of cannabis is “strongly linked to the development of psychosis”. In fact, the authors suggest that cannabis consumption may be responsible for increasing the risk of developing psychotic disorders by almost 5 times.

In the article, the researchers report that the odds of developing psychosis are strongly influenced by the frequency of use and potency of the cannabis product, therefore establishing a correlation between cannabis use and the development of psychosis.

However, the conclusions of this study have already been disputed by other scientists.

In another article recently published in The Lancet, Nathan Gillespie and his colleagues refuted the conclusions presented by Di Forti, referring that the researchers responsible for the study have assumed “cannabis causes psychosis or psychotic symptoms without acknowledging compelling and alternative hypotheses”.

In summary, the authors of this dispute alert to a common mistake that is made in the scientific community: mistaking correlation for causality. In other words, the fact that two things are somehow related doesn’t necessarily mean that one causes the other.

According to Gillespie, there is evidence that points to the fact that individuals who already have a genetic predisposition to developing psychosis may also have a higher predisposition to cannabis use. That means that people who are naturally predisposed to psychotic conditions are more likely to use cannabis, not the other way around.

Gillespie and his colleagues refer that Di Forti and her team didn’t consider all the relevant parameters for their study and that their conclusions may not be correct. “By not acknowledging the alternative, compelling, and plausible mechanisms, the conclusion regarding the harmful effect of high-potency cannabis use on mental health is likely to be overestimated”, they add.

The initial study linking cannabis use and psychosis development, as well as its dispute by Gillespie and his team, both clearly reflect one the major issues regarding the studies about cannabis consumption.

The fact is that these results may be influenced by a series of political and social misconceptions that need to be carefully addressed and evaluated.

In fact, Kira London-Nadeau, a graduate student at the University of Montréal and head of the Canadian Students for Sensible Drug Policy network, recently commented on this issue to the press.

According to London-Nadeau, when scientists’ conclusions are based on this “very simplistic and very scary” idea, it means that a very specific logic is being implied. “That if cannabis were not around, we wouldn’t have these mental-health issues”, she adds.

Moreover, she also alerts to a very important fact: this message, although it “speaks to people so easily”, is not “the whole picture and it isn’t the truth”.

Gillespie and his colleagues agree with this point of view and are not the only ones. In fact, there are reports pointing to the use of cannabidiol (CBD), a cannabis compound, being linked to a decrease in psychotic episodes.

The source of this issue has once been explained by David Nutt, drugs expert, and professor of Neuropsychopharmacology in the Imperial College of London. According to Nutt, cannabis has been used as medicine for the past 3,000 years, across many different ancient civilizations. Cannabis’ use as medicine was normal until the early 1930s when a political issue arose, and the US Senate labelled cannabis as a “dangerous drug”.

This label has spread around the US and Europe for decades and is now slowly starting to be analyzed and dismantled. Although it may take some time to erase the fear that has been planted around cannabis use, steps are now being taken as scientists begin to rationally and clearly analyze the impacts of cannabis consumption and cultivation.

As more scientific discoveries are made regarding the way cannabis and its components work on the human body and what possible benefits they may have on public health, also the misconceptions from the past begin to emerge and to be clearly identified and corrected. These events represent a clear evolution towards a better understanding of cannabis and cannabis-related products.


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