Via: Ollyy | Shutterstock

Study Debunked: No, Marijuana Does Not Cause Psychosis

Via: Ollyy | Shutterstock


by Ben Miller

on June 2, 2015

This story first appeared in Cannabis Now Magazine.

The newest in what some would consider to be a long line of media smear campaigns against marijuana and cannabis use arose out of The Daily Mail.

The article outlines a study published in the British medical journal The Lancet, which claims that British citizens who smoke what they refer to as “skunk” marijuana are three to five times more likely to develop psychosis in their lifetime.

Like any good smear campaign, the article made a lot of its readers quite scared that the report could be true and that their children are out on the streets destroying their mental health with extremely high-potency weed.

American outlets like Fox News and Yahoo News quickly picked up on the story and reported it in the U.S., where marijuana legalization has become a hot topic issue. Amongst the debate over marijuana, one of the biggest issues being discussed right now is the long-term effect that it has on the mind and body.

These reporters took the story and ran with it, sparing no time to do any fact checking on the original story or the study itself. But thankfully, Paul Armentano, Deputy Director of NORML, decided to do just that.

After the original article was posted, Armentano published a rebuttal to the study on Alternet, where he essentially reveals the article for what it is: nothing more than a poorly-executed example of what’s wrong with the current state of marijuana research that’s been twisted into a scary news story used to distract readers from the truth of the matter.

At first the study seemed fairly straightforward and legitimate. It took place over six years (from 2005 to 2011) and utilized 780 people as test subjects between the age of 18 and 65. Approximately 370 were citizens off the streets who were used as a control set and 410 were psychiatric patients who had claimed to have had first-episode psychosis.

potent viaGROGL


The scientists asked the two groups of subjects about their marijuana smoking habits and based their findings on the answers given.

According to the study, which was led by Marta Di Forti from the Institute of Psychiatry, Psychology, and Neuroscience at King’s College London, those who had suffered from psychosis were more likely to have used what they call “skunk-like cannabis” on a daily basis. But those subjects who claimed that they were more likely to smoke what the study calls “hash,” or a less potent marijuana extract, didn’t suffer from the psychological maladies that the others had.

What seems to be a fairly standard scientific study begins to smell a little fishy when you look into the details of the study itself. To begin with, Armentano points out that the study lacks any kind of regulation for their extremely loose definitions of what they consider to be kinds of marijuana.

Armentano writes: “Researchers defined so-called skunk marijuana as cannabis possessing THC concentrations above 15 percent. Of course, since cannabis is illegal in Britain and the weed obtained on the black market is not subject to analytical potency testing, it is unclear how subjects in the study — or its authors — knew whether participants were consuming supposed ‘high potency’ herb or just regular plain old weed.”

Similarly, Mitchell Colbert from The Leaf Online also reported on the inconsistencies within this study. Colbert explains that the definitions the researchers use are “so inaccurate they are actually laughable.” He explains that “skunk” is not a specific kind of marijuana, but “a strain of cannabis” that “are known to be potent,” but no more so than any other high-grade strain of cannabis.

Additionally, Colbert points out that what the researchers refer to as “hash,” or what they consider to be a “low-potency resin,” is actually a misnomer. Hash, according to Colbert, is “a very high potency concentrated form of cannabis, which can be derived from skunk or any other strain.”

Even beyond these two terms, it’s clear through the report that the researchers weren’t able to correctly or effectively create definitions for any of the terminology that they used throughout the experiment.

Armentano continues his rebuttal by explaining that the researchers did not fully utilize all of the information that they found during the study to derive their conclusion. The authors of the study admitted that they discovered that in those subjects who suffered from first-episode psychosis also admitted to “having smoked 100 cigarettes or more,” showing that important aspects of the patients’ mental health were intentionally left out of the results.

And because all of the data collected by the scientists was “self-reported” by the subjects, there’s no way for the research team to accurately collect any set of data without compromising the integrity of their control set. With self-reported data collection, scientists usually take steps to prevent any inaccuracies that may occur, but there are no mentions of any of these steps being taken by the scientists.

On top of all of this, a study out of Harvard University, published in the 2013 issue of Schizophrenia Research, effectively rebuts the King’s College study by showing that “a family history of schizophrenia increased the risk of developing the disease, regardless of whether or not subjects consumed weed as adolescents.”

The cherry on top of it all was when senior researcher Sir Robin Murray, a psychiatric research professor at King’s College, forgot one of the most important rules of scientific study: correlation does not equal causation. Sir Murray released a statement with the study, claiming that “This paper suggests that we could prevent almost one-quarter of cases of psychosis if no one smoked high-potency cannabis.”

Overall, this study simply seems to be the next big scare campaign against the use of marijuana from its legal and scientific opponents. However, this study has made it clear that marijuana research can very easily go unregulated and grossly inaccurate in its execution, leading to misinforming of the masses. If more studies like this arise, then it will become more and more difficult for normal citizens to understand the truth about how marijuana affects them — both on a mental and physical level. Hopefully, in the near future, steps will be taken to help regulate these studies and stop more smear campaign stories like this from arising.