Agroup of 75 scholars and medical professionals have criticised a controversial new book about the purported dangers of marijuana, calling it an example of “alarmism” designed to stir up public fear “based on a deeply inaccurate misreading of science”.
Berenson argues that proponents of marijuana use have ignored evidence that the drug’s active compound, THC, may precipitate the onset of schizophrenia and provoke acts of violence in individuals who experience a psychotic “break”.
On Friday, 75 scholars and clinicians signed an open letter, joining a chorus of disagreement with Berenson by arguing that “establishing marijuana as a causal link to violence at the individual level is both theoretically and empirically problematic”.
The signatories include academics from New York University, Harvard Medical School and Columbia University and care providers including addiction medicine doctors, psychologists, psychiatrists and social workers.
“We urge policymakers and the public to rely on scientific evidence,” they wrote, “not flawed pop science and ideological polemics, in formulating their opinions about marijuana legalization.”
In a statement to the Guardian, Berenson dismissed the letter, arguing that it “attracted only a handful of signatures from MDs, and almost no psychiatrists, who are on the front lines of treating psychosis and severe mental illness”.
“I am not surprised,” he said. “Physicians know the truth.”
‘The evidence guides your position’
The correlation between chronic mental illness, specifically schizophrenia, and marijuana use is widely accepted in scientific literature. Where the agreement ends is on the issue of causality.
Most research falls well short of Berenson’s certainty, which he primarily bases on two studies. One is by a Swedish researcher who in 1987 concluded that “cannabis is responsible for between 10% and 15% of schizophrenia cases”. The other, published by the National Academy of Medicine in 2017, found that “cannabis use is likely to increase the risk of developing schizophrenia and other psychoses; the higher the use, the greater the risk”.
The latter report, Berenson wrote in the New York Times last month, “declared the issue settled”. That claim was in turn rebutted by Ziva Cooper, a study board member, who argued in a series of tweets that researchers merely “found an association between cannabis use and schizophrenia”.
Cooper, who directs the Cannabis Research Initiative at UCLA, wrote: “Since the report, we now know that genetic risk for schizophrenia predicts cannabis use, shedding some light on the potential direction of the association between cannabis use and schizophrenia.”
The reaction from people in the advocacy and science community, I’m surprised by their intellectual dishonesty,
Writing for Vox, the reporter German Lopez noted: “Far from declaring this issue ‘settled’, the National Academy’s report was extremely careful, cautioning that marijuana’s – and marijuana addiction’s – link to psychosis ‘may be multidirectional and complex’. Marijuana may not cause psychosis; something else may cause both psychosis and pot use. Or the causation could go the other way: psychotic disorders may lead to marijuana use, perhaps in an attempt to self-medicate.”
One 2010 review of studies on the topic declared: “The contentious issue of whether cannabis use can cause serious psychotic disorders that would not otherwise have occurred cannot be answered from the existing data.”
Even those who lean towards Berenson’s position tend to show restraint.
One of the most certain findings against Berenson’s position, meanwhile, comes from Dr Carl Hart, a drug and addiction researcher at Columbia.
In 2016, he concluded: “Cannabis does not in itself cause a psychosis disorder. Rather, the evidence leads us to conclude that both early use and heavy use of cannabis are more likely in individuals with a vulnerability to psychosis.”
Speaking to the Guardian, Hart said he was frustrated by even the framing of the question.
“I’m not playing that dumb game that we usually play in the media, like ‘There’s one side here, there’s one side there,’” he said. “In science it doesn’t work that way. The evidence guides your position.
“It’s a bullshit claim. There’s not evidence for it.”
‘He’s clearly an advocate’
In Tell Your Children, Berenson anticipates resistance. “I know what a lot of you are thinking right now,” he writes. “This is propaganda. Marijuana is safe. It’s what you’ve been told for the last 25 years. I once thought it, too.”
He selected the title for the book after anticipating, correctly, that it would be compared to the now widely-mocked 1936 film Reefer Madness, which depicts teens descending into violent insanity. Tell Your Children was the film’s original name. Nonetheless, he told the Guardian he has been surprised by his book’s reception.
“The reaction from people in the advocacy and science community, I’m surprised by their intellectual dishonesty,” Berenson said.
In response, Berenson has become increasingly active on Twitter, posting links to crimes committed by people with marijuana in their system, goading his critics and repeating the mantra: “Cannabis causes psychosis. Psychosis causes violence.”
In conversation, he says he sees himself lining up opposite a well-resourced foe, as monied elites, shielded by a faux-counterculture veneer, line up to make a buck. “It’s like the rebels seized power and they didn’t even realize it,” he said. “They have the media, they have an industry, they have financing, they have everything.
“Unfortunately, I feel like in defending the facts, I’ve been pushed a little bit into being an advocate, which is not where I want to be. I want to be a journalist.”
Some think Berenson crossed that line long ago.
“He’s clearly an advocate,” said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (Norml). “He has a biased view. He cherry picks the science that he thinks fits his agenda and he disregards the science that doesn’t.”
That is a common claim from Berenson’s critics on both the issue of schizophrenia and on his claims that states which have fully legalized marijuana have experienced a demonstrable spike in crime, the other primary argument in his book.
In return, he sees his critics as advocates defending ideological positions even as science says otherwise.
He cites as an example Issac Campos, an associate professor of history at the University of Cincinnati and a signer of the letter. Berenson cited his work in a passage about attitudes towards marijuana in Mexico in the early 20th century.
After Campos told Vox that Tell Your Children “pretty badly misrepresented” his argument, Berenson told the Guardian: “I’m sorry that [Campos’] ideology doesn’t let him see what his research found, which is pretty amazing.”
‘Just tell the truth’
Although debates on the science of the issue are profound, to some degree Berenson and many of his critics seem to be arguing past each other.
He wants marijuana legalization advocates to concede that the drug carries real risks; Armentano said that is something they readily do.
“Norml is very up front and always has been that cannabis is not innocuous, and that marijuana poses particular risks,” said Armentano. “Berenson is not somehow playing ‘gotcha’ with a group like Norml by trying to highlight or identify the fact that there may be certain apps at risk populations for cannabis.”
Advocates, meanwhile, want Berenson to contend with what they perceive as the failures of marijuana prohibition.
In the open letter posted on Friday, the researchers and clinicians wrote: “Weighed against the harms of prohibition, including the criminalization of millions of people, overwhelmingly black and brown, and the devastating collateral consequences of criminal justice system involvement, legalization is the less harmful approach.”
Berenson is open to that position – although he doesn’t agree with it.
“You can believe that cannabis is a real risk for psychosis and violence and still believe it should be legal,” he said. “That’s a totally reasonable position to take. Just tell the truth.”