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This article was published 14/1/2019 (576 days ago), so information in it may no longer be current.
Using cannabis can cause psychosis such as schizophrenia, and psychosis can cause violence, therefore, marijuana use can cause violent crime.
That's the frightening argument made by former New York Times reporter and spy novelist Alex Berenson in his new book, Tell Your Children: The Truth About Marijuana, Mental Illness, and Violence, which has received huge publicity in the U.S. since it was published by Simon and Schuster this month.
But the science exploring the causal link between cannabis and psychosis is far more nuanced — and far less conclusive — than Berenson claims in his torqued-up, alarmist narrative.
Readers expecting journalistic rigour or impartiality from a journalist such as Berenson will be disappointed. At the very least, he freely acknowledges in the prologue that Tell Your Children is not balanced, which, he writes, doesn't mean the book is "inaccurate, dishonest, or in any way untruthful."
Dishonest or not, Berenson's book is riddled with hyperbole and questionable logic. His argument is built on carefully selected nuggets from the existing body of research on cannabis and psychosis, but it doesn't give equal credence to high-quality competing evidence. He represents the scientific literature on the subject in a way that wrongly suggests the case is closed.
Take the comprehensive 2017 review of the health effects of cannabis from the prestigious National Academies of Sciences, Engineering, and Medicine (NASEM). Berenson holds this up as a smoking gun, claiming NASEM examined the research (on cannabis and psychosis) "and declared the issue settled."
The NASEM report did indeed say, "Cannabis use is likely to increase the risk of developing schizophrenia and other psychoses," which Berenson quotes verbatim. (Indeed, that quote is the very first bullet point in the report's chapter on cannabis and mental health.) But anyone who reads the entire chapter learns that NASEM never concluded that cannabis use, on its own, actually causes schizophrenia.
Dr. Ziva Cooper, who served on the NASEM committee that conducted the review, has recently taken to social media to explain this.
Berenson genuinely believes marijuana can cause schizophrenia in a minority of users, even if they don't have pre-existing risk factors for the disorder.
"When you increase the risk of something, you are causing cases of something that wouldn't otherwise happen," he said in an interview.
"That's math. I'm not saying that that's a lot of cases... But when you increase the risk of something, you're causing de novo cases. I don't understand, actually, why this is a complicated argument to follow."
Berenson's interpretation of the research is out of step with scientific consensus, according to neuroscientist Matt Hill, an associate professor with the University of Calgary's Mathison Centre for Mental Health Research and Education, who studies the human endocannabinoid system.
"I can tell you that 90 per cent of the people in (the field of cannabinoid research) do not believe this, and the only ones who believe this causal relationship are, essentially, a scattering of psychiatrists," said Hill, who hasn't yet read Tell Your Children but has been debating Berenson via email in response to op-eds he's written promoting his book in The Wall Street Journal and The New York Times.
Dr. Peter Grinspoon, a Harvard Medical School instructor and a board member of the pro-legalization group Doctors for Cannabis Regulation, also thinks Berenson's argument is misleading.
"He's making it sound like there's consensus that cannabis causes schizophrenia," said Grinspoon.
"We know that it's associated. It has always been associated. But we just don't know that cannabis causes schizophrenia. It could be that cannabis causes schizophrenia. It could be it's bi-directional."
Berenson insists Tell Your Children is a medical and scientific book, but the volume doesn't include any footnotes or endnotes that might help readers evaluate the research on their own.
Tell Your Children
The Truth About Marijuana, Mental Illness, and Violence
By Alex Berenson
Free Press, 272 pages, $35
"I don't think I anticipated that people would want that, because I see it as a book for a lay reader," Berenson said.
It's not hard to imagine that those casual readers could be bamboozled by the research Berenson chooses to present, as well as his insistence that correlation equals causation.
"It's written so manipulatively that I think it takes advantage of people who don't understand science or statistics," said Grinspoon.
"I don't think he understands the complications of interpreting statistical associations with something like cannabis, where you have a very complicated relationship with mental illness," Hill said.
Berenson's questionable presentation of the evidence in Tell Your Children even extends to historical interpretation. As proof that the marijuana-psychosis link isn't just anti-drug propaganda dreamed up by the U.S. during the Reefer Madness era, Berenson cites Home Grown: Marijuana and the Origins of Mexico's War on Drugs, a 2012 book by historian Isaac Campos that explores Mexicans' historical attitudes towards the drug.
"He claims, based on my work, that Mexicans had no cultural reason to view marijuana negatively," wrote Campos in an email after reviewing the relevant passages from Tell Your Children.
"I actually argue just the opposite, which leads me to suspect that he didn’t read the book very carefully."
Tell Your Children is already making waves in the United States. Aside from his plum placements in the op-ed pages of the Times and the Journal, the book received a favourable write-up in The New Yorker by none other than the patron saint of counterintuitive mass-market social science himself, Malcolm Gladwell.
Even if many experts disagree with Berenson's interpretation of the data, there's no denying that "cannabis causes psychosis" is a sexy narrative that sells.
"The lesson here is that journalists should know their limitations," said Mark Kleiman, a New York University professor of public policy who takes issue with the way Berenson deploys crime statistics to support his argument. (New York Magazine writer Jesse Singal has neatly debunked Berenson's claims of a cannabis-fuelled crime wave in the U.S.)
"I think (Berenson) doesn't know what he doesn't know, which is true of most of us," said Kleiman.
Unsurprisingly, Berenson's ultimate conclusion in Tell Your Children is that marijuana shouldn't be legalized in the United States. (He favours decriminalization.)
"If you are an average American, you believe both medical and recreational marijuana should be legal," he writes in the epilogue.
"I'm trying to change your mind. And changing someone's mind is next to impossible. I mean anyone's mind, of anything. People think what they think. So, this book all by itself may not do much."
That's probably true. But Berenson's book would stand a much better chance at changing readers' minds if it presented anything in the way of new, compelling evidence that cannabis causes schizophrenia.
The scientific and medical community doesn't deny the statistical connection between cannabis and schizophrenia: there's clearly a relationship between the two, and it's safe to say that people at risk for schizophrenia should avoid the drug.
Conscientious research that actually clarifies the nature of that link would be welcome. Tell Your Children isn't it.
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