The idea of marijuana causing a psychotic breakdown sounds like something out of the camp film classic "Reefer Madness", but many experts argue it's not that far-fetched.
As legalisation of recreational marijuana spreads across the United States, more people are showing up in ERs with psychotic symptoms after consuming too much pot, said Dr Itai Danovitch, chairman of psychiatry and behavioural neurosciences at Cedars-Sinai in Los Angeles.
Full-fledged psychotic disorder
"If somebody gets too high, they use more than intended, they can have psychotic symptoms. That typically resolves as the drug wears off," Danovitch said. "After it's worn off, there's no subsequent psychosis. That's just a direct effect of over-intoxication."
But some unlucky souls with a family history of mental illness might wind up with a full-fledged psychotic disorder that will require extended treatment, Danovitch noted.
"That risk is concentrated among a minority of people who have an existing vulnerability to develop a psychotic disorder, a family history of psychosis," Danovitch said. "There are environmental factors that influence whether somebody develops schizophrenia who has a risk. It appears cannabis probably is one of those factors."
Vaping a potent form of THC – the intoxicating ingredient in pot – prompted a psychotic episode last year in 24-year-old Madison McIntosh of Scottsdale, Ariz., according to USA Today.
McIntosh appeared at the driving range where he worked on his day off, wandering around and talking babble for 12 hours straight. His family rushed him to a hospital, where he told his father that he was seeing double rainbows. Doctors diagnosed him with cannabis use disorder and unspecified psychosis.
McIntosh remembers feeling "out of it, delusional" at the driving range, where he thought people were following him. "I was pretty scared," he told USA Today of the March incident. "I didn't know where I was at."
Strong causal relationship
Despite anecdotes like these, sceptics argue that the science on a potential link between pot and psychosis remains far from solid.
"It would appear to be premature, at best, and sensational, at worst, to opine that a strong causal relationship exists between cannabis exposure and psychiatric disorders, given the lack of consensus among experts in the field and the fact that rates of psychosis and mental illness have largely remained static over the decades while at the same time rates of cannabis use have fluctuated dramatically," said Paul Armentano. He is deputy director of NORML, a non-profit calling for the reform of marijuana laws.
"This latter fact undermines the theory that cannabis exposure is a direct cause of psychiatric illness in otherwise non-predisposed subjects, and instead indicates that those most likely to express psychotic symptoms possess a predisposition to both cannabis use and psychotic behaviours," Armentano added.
Still, a study published recently in the Lancet journal found that daily marijuana use may increase the risk of a first-time psychotic episode by three to five times, depending on the potency of the pot.
The Lancet study reported that in the three sites with the greatest consumption of high-potency cannabis, daily use of high-potency cannabis was associated with the greatest increase in the odds for psychotic disorder – four times greater in Paris, five times greater in London, and more than nine times greater in Amsterdam.
These temporary psychotic episodes are "not a common marijuana experience, but it's common given how prevalently marijuana is used," Danovitch said.
The risk of so-called "transient psychosis" has grown with both the increasing potency of new pot strains and the increased use of edible marijuana products, said Dr Scott Krakower, assistant unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, New York.
"You can ingest a large amount of high-potency agents in a quick period of time," Krakower explained. "It's not going to take you a lot with edibles to hit a very high dose of marijuana. If you're not regulating yourself, you could go up pretty fast without even realising it."
But there's a small proportion of people whose existing vulnerability to mental illness makes them more likely to have lasting psychosis if they use too much pot, studies have found.
The risk for schizophrenia following substance-induced psychosis is about 11%, with the strongest association among vulnerable users of pot, according to a 2019 study in the American Journal of Psychiatry.
Danovitch said he counsels young people to consider their genetic risk for mental illness before they use marijuana.
"If they have a family history of serious mental illness, their risk may be really different from that of their peers," Danovitch said. "It's important that they be aware and informed about that."
Harms amplified in adolescents
Emily Feinstein, executive vice president at the Center on Addiction, seconded those concerns regarding young users.
"The research is clear that adolescent marijuana use is associated with an increased risk of schizophrenia or psychotic symptoms in young people with a potential vulnerability to mental illness," Feinstein said.
"The harms of marijuana are amplified in adolescents and young adults, whose developing brains are more vulnerable to the impact of THC," she noted. "Parents should be especially concerned if their children are using high-concentrate THC products."
Armentano agreed that the "growing concerns over this potential relationship ought to be taken seriously and they provide an argument in favour of better regulation of the plant so that it can be better kept out of the hands of young people and so that targeted warnings be directed toward those adults who may be at higher risk for an adverse reaction.
"Maintaining cannabis prohibition, unfortunately, achieves neither result," Armentano said.
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