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Cannabis-Induced Psychosis: Real or Reefer Madness?

May 22, 2018
Reefer Madness promotional poster. (George A. Hirliman Productions)
Last year, a personal injury lawyer attacked a family of immigrants in the parking lot of an Ontario mall because they were speaking Spanish. He accused one man of being a terrorist and broke his ribs with a baseball bat.

There is disagreement about whether cannabis can cause transient psychotic episodes in otherwise healthy people.

The Toronto-based lawyer, Mark Phillips, pled guilty to assault but claimed he was suffering from cannabis-induced psychosis. The court gave him a conditional discharge. After serving three years’ probation and doing some community service, he won’t have a criminal record.

Critics denounced the sentence as too lenient and were quick to note that Phillips is the great-grandson of Nathan Phillips, the late Toronto mayor after whom a public square is named. (Nathan Phillips Square forms an expansive courtyard in front of Toronto City Hall.)

The incident also renewed debate about cannabis and psychosis.


Cannabis and Mental Health: It’s Complicated

Cannabis consumption has been associated with psychotic behaviour since the 1930s, when audiences were introduced to Reefer Madness. In the 68-minute film, high school students descend into madness after smoking cannabis.

In Quebec, the perceived threat of cannabis psychosis has been presented as evidence to support its prohibition.

More recently, the perceived threat of cannabis psychosis has been presented as evidence to support its prohibition: In an interview with CBC/Radio-Canada last year, Quebec’s health minister Gaétan Barrette noted that cannabis “can induce a deterioration of mental state all the way to causing psychosis” in people who are biologically predisposed, adding that “nobody has ever [experienced] psychosis on alcohol.”  That elicited groans across the province and beyond; the link between alcohol and psychosis has been well-documented.

Is there a comparable link between cannabis and psychosis? Some experts say cannabis consumption can cause mental illnesses that feature psychosis but others disagree. There is also disagreement about whether cannabis can cause transient psychotic episodes in otherwise healthy people.


Cannabis and Schizophrenia: Do THC and CBD Affect It Differently?

In a 1987 study, researchers found that Swedish conscripts had an increased risk of developing schizophrenia if they had consumed cannabis more than 50 times in their lives. Since then, other researchers have also found an intricate relationship between cannabis and mental illness — and concluded that cannabis use increases the risk of developing mental disorders.

Evidence indicates cannabis can promote the onset of schizophrenia in people with a biological predisposition to it— individuals who would probably develop the mental disorder anyway.

But other experts take issue with that hypothesis. There may be an intricate relationship between cannabis and mental illness, they say, but that is not proof that cannabis causes mental illness.

In 2015, Matthew Hill of the Hotchkiss Brain Institute at the University of Calgary wrote an article for the journal Nature, in which he said there is little evidence of a causal relationship. He went further, saying there is evidence that cannabis use does not cause schizophrenia.

However, he added that evidence indicates cannabis can promote the onset of schizophrenia in people with a biological predisposition to it— individuals who would probably develop the mental disorder anyway.

“Imagine that [schizophrenia] is like a campfire,” he wrote. “Adding fuel to a pile of sticks has little effect, but throwing fuel on a weakly burning fire will increase its strength. Regardless of whether fuel is added, the embers will continue to burn.”


Cannabis and Depression

Dr. Romina Mizrahi, director of the Focus on Youth Psychosis Prevention Clinic at The Centre for Addiction and Mental Health in Toronto told Leafly that “cannabis could be a trigger of an underlying condition.”  She added that, although “there is a proven link between cannabis and psychotic experience,” the link is only proven in young people — whose brains are still developing — and it remains unclear “who will experience those symptoms or when.”

“The argument that cannabis can cause psychosis is not based on sound scientific evidence. Causation has not been proven.”
Paul Armentano, deputy director of NORML

Many experts speculate that cannabis use is not the cause of mental illness but rather the byproduct of it — that people who have psychotic episodes use cannabis to self-medicate before they are ever diagnosed with mental illness.

Hill and other experts say clinical studies have shown that pure THC can produce a temporary psychotic state in people who don’t have mental illness — but not everyone is convinced.

“The argument that cannabis can cause psychosis is not based on sound scientific evidence. Causation has not been proven,” Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (NORML),  told Leafly. “It is our position that the relationship between cannabis and psychosis is not well-defined or well-understood.”

There is a lot of debate about whether Mark Phillips was in a cannabis-induced psychotic state when he swung his bat at Sergio Estepa yelling, “ISIS!” but there is much less debate about whether that was an adequate defence.

“My presumption is that if someone knowingly engages in substance that alters mood or behaviour, how can it be excusable?” said Armentano. “That is like saying that, if I hadn’t consumed so much alcohol, I wouldn’t have done this — so my actions were excusable.”

Added Dr. Mizrahi, “How could a man of Mr. Phillips’s education and training as a lawyer not have been aware of the effects of cannabis before using it?”

Randi Druzin's Bio Image

Randi Druzin

Randi Druzin is an author and journalist in Toronto. She has worked at several major media outlets, including the National Post and the CBC, and has written for dozens of publications, such as The New York Times, Time magazine, ESPN The Magazine, and The Globe and Mail.

View Randi Druzin's articles

  • Mo Jo

    If you are a Type-A personality with anger issues who barely has a lid on things, and you consume drugs, you may find yourself losing your barely controlled inhibitions and then unloading on someone. It’s not the drugs, it’s you. It was only a matter of time.

    • Eclectic Duality

      Thank you for your rationale and logic, quite refreshing.



    • Mark Higham

      No kidding , pampered rich kid gets away with criminal behaviour and avoiding a life crippling criminal record ….no justice when you have the privileged standing accused and in the court room . Legalise now , around the globe , Legalise all ✌️☮️✌️

      • ALAN GANN
        • kungfuninja

          Cannabis IS safer than your government. The problem, though, is that most of the people who are actively trying to get it legalized are the same leftist liberals that want the government regulating every other aspect of our lives. There are some libertarians (like me) who want the government to just leave us alone as long as we aren’t hurting others, but most are just big government hippie liberals who want to smoke pot and get the government to make other people pay if they end up lazy and poor. It’s a sad state. 🙁

          • ALAN GANN


          • kungfuninja

            Ok, I’m not talking about disabled veterans. For sure the government should take care of them. We are definitely in agreement!

  • P.J. Rafter

    Sheeesh! The outright lies just keep on coming…

    • Von

      The lies are easily disputed based on historical usage rates vs. rates of diagnosed mental illness…

  • Highway 69

    Blaming your criminality on something other than yourself has been a go-to defense for ages. Cannabis was a convenient excuse for his own hatred to be put on the world stage.

  • Kevin Dennis

    Let’s compare this lawyer’s argument to gun violence. A person committing a violent act can no more blame cannabis than a person committing a violent act with a gun can blame the gun.

  • Oh yeah, I remember all the hippies at the Grateful Dead concerts swinging bats and shouting the names of terrorist organizations to the four winds. /s

    The real bat in this story is the bat$41t crazy dude claiming MJ gave him temporary psychosis. Reefer Madness isn’t a documentary, people.

    • Doris

      not to mention the 500,000 kids in the rain and mud soaked fields of Woodstock’s 1969 concert, all without shelter nor food…;?)

      Try that with alcool.

      • Jim Lunsford

        Well, the brown acid calmed them down. Else it would have been (reefer) madness!

  • 360dunk

    Quebec’s health minister Gaétan Barrette sounds like a brainwashed, programmed government stooge who has no idea how cannabis works. Then again, this is the same idiotic government that kept shutting down Rick Simpson as he was helping thousands of Canadians with their cancer battles. NEVER accept the manure that those in charge are spreading about marijuana because they know nothing.

  • Laura P. Schulman

    An easy out, for someone who has impulse control problems, to blame the herb for their own native assholery. Part of this creep’s punishment for maligning the herb should be a permanent, forever ban on his presence anywhere herb is sold or consumed.

  • ElleGee

    Stop the Lies! Legalize!

    • Jim Lunsford

      Decriminalize. Make the law recognize it’s just a plant and they have no power to regulate it. Or just ignore the law like everyone here already does. Except you in those legal states.

  • Thomas Petcher

    I think if taken wiith other strong drugs cannabis can be a catalyst for Drug Induced Psychosis. To think cannabis can’t be harmful to people is just wishful thinking, i know friends who have suffered from it, but they all abused other drugs such as stims and psychedelics, cannabis helped push them over into Audiotory hallucinations and full blown psychosis.

    In the main it’s safer than most, if abused, but not harmless.

  • Von

    There is an obvious flaw in the theory that cannabis causes mental illness… general population rates of mental illness vs. useage rates. In 1968 only 4% of the population admitted to using cannabis at least once, while diagnosed with some sort of mental illness was 26% of the population. In 2015, 52% of the US population had used cannabis at least once, with 12% considered regular consumers, while mental health diagnosed illness decreased to 20%. The useage rate went up 1150%, while mental illness decreased. Even if you conservatively approach this from heavy users, the increase in use was 300%. If using cannabis had anything to do with causing mental illness, mental illness diagnosis would have at the very least increased to 30% to 70% of the population with mental illness. Math as follows: 26% 1968 mental illness -4% of marijuana users at the time (assuming that those users were mentally ill, +8% of increase in regular users to a minimum of 30% with mental illness today. Apply the same numbers for anytime user and you should see (26%-4%+48%)=70% of the population with mental illness. But NO!!! We saw a decrease, please explain how cannabis causes mental illness if use went up yet mental illness decreased…

    I personally think that the relationship they are seeing with mental illness and drug use is more self treatment and or perceived risky behavior from being mentally ill to begin with.

  • Buzzby19491

    “Cannabis psychosis” seems to have a lot to do with political history. Reports of cannabis psychosis only come from the UK and British Commonwealth nations. We had something similar in the US. It was called “Reefer Madness” and was based on a 1936 propaganda film. The film has been popular here since the late ’60s as an over-the-top comedy. One has to ask whether “cannabis psychosis” is anything more than “reefer madness”, mildly updated for the 21st century.

  • SocialismWorks

    No one has ever committed a crime under the influence of alcohol. Plus it cures mental illness and makes you healthier.
    Another round for my friends!

    • Calamity_Jean


  • weedy454

    What about legal alcohol and its effects on the mind??????¿??