For indispensable reporting on the coronavirus crisis, the election, and more, subscribe to the Mother Jones Daily newsletter.

It’s been a few years since Alex Berenson has “committed journalism,” as he likes to say. As a New York Times reporter, Berenson did two tours covering the Iraq War, an experience that inspired him to write his first of nearly a dozen spy novels. Starting with the 2006 Edgar Award-winning The Faithful Spy, his books were so successful that he left the Times in 2010 to write fiction full time. But his latest book, out January 8, strays far from the halls of Langley and the jihadis of Afghanistan. Tell Your Children is nonfiction that takes a sledgehammer to the promised benefits of marijuana legalization, and cannabis enthusiasts are not going to like it one bit.

The book was seeded one night a few years ago when Berenson’s wife, a psychiatrist who evaluates mentally ill criminal defendants in New York, started talking about a horrific case she was handling. It was “the usual horror story, somebody who’d cut up his grandmother or set fire to his apartment—typical bedtime chat in the Berenson house,” he writes. But then, his wife added, “Of course he was high, been smoking pot his whole life.”

Berenson, who smoked a bit in college, didn’t have strong feelings about marijuana one way or another, but he was skeptical that it could bring about violent crime. Like most Americans, he thought stoners ate pizza and played video games—they didn’t hack up family members. Yet his Harvard-trained wife insisted that all the horrible cases she was seeing involved people who were heavy into weed. She directed him to the science on the subject.

We look back and laugh at Reefer Madness, which was pretty over-the-top, after all, but Berenson found himself immersed in some pretty sobering evidence: Cannabis has been associated with legitimate reports of psychotic behavior and violence dating at least to the 19th century, when a Punjabi lawyer in India noted that 20 to 30 percent of patients in mental hospitals were committed for cannabis-related insanity. The lawyer, like Berenson’s wife, described horrific crimes—including at least one beheading—and attributed far more cases of mental illness to cannabis than to alcohol or opium. The Mexican government reached similar conclusions, banning cannabis sales in 1920—nearly 20 years before the United States did—after years of reports of cannabis-induced madness and violent crime.

People who used cannabis at 15, one study found, were more than four times as likely to develop schizophrenia or a related syndrome.

Over the past couple of decades, studies around the globe have found that THC—the active compound in cannabis—is strongly linked to psychosis, schizophrenia, and violence. Berenson interviewed far-flung researchers who have quietly but methodically documented the effects of THC on serious mental illness, and he makes a convincing case that a recreational drug marketed as an all-around health product may, in fact, be really dangerous—especially for people with a family history of mental illness and for adolescents with developing brains.

A 2002 study in BMJ (formerly the British Medical Journal) found that people who used cannabis by age 15 were four times as likely to develop schizophrenia or a related syndrome as those who’d never used. Even when the researchers excluded kids who had shown signs of psychosis by age 11, they found that the adolescent users had a threefold higher risk of demonstrating symptoms of schizophrenia later on. One Dutch marijuana researcher that Berenson spoke with estimated, based on his own work, that marijuana could be responsible for as much as 10 percent of psychosis in places where heavy use is common.

These studies are hardly Reagan-esque, drug warrior hysteria. In 2017, the National Academies of Sciences, Engineering, and Medicine issued a report nearly 500 pages long on the health effects of cannabis and concluded that marijuana use is strongly associated with the development of psychosis and schizophrenia. The researchers also noted that there’s decent evidence linking pot consumption to worsening symptoms of bipolar disorder and to a heightened risk of suicide, depression, and social anxiety disorders: “The higher the use, the greater the risk.*”

Given that marijuana use is up 50 percent over the past decade, if the studies are accurate, we should be experiencing a big increase in psychotic diseases. And we are, Berenson argues. He reports that from 2006 to 2014, the most recent year for which data is available, the number of ER visitors co-diagnosed with psychosis and a cannabis use disorder tripled, from 30,000 to 90,000.

If pot was as widely used as alcohol, one researcher said, “we would see an enormous amount of morbidity from cannabis.”

Legalization advocates would say Berenson and the researchers have it backwards: Pot doesn’t cause mental illness; mental illness drives self-medication with pot. But scientists find that theory wanting. Longitudinal studies in New Zealand, Sweden, and the Netherlands spanning several decades identified an association between cannabis and mental illness even when accounting for prior signs of mental illness. In an editorial published alongside the influential 2002 BMJ study on psychosis and marijuana, two Australian psychiatrists wrote that these and other findings “strengthen the argument that use of cannabis increases the risk of schizophrenia and depression, and they provide little support for the belief that the association between marijuana use and mental health problems is largely due to self-medication.”

One of the book’s most convincing arguments against the self-medication theory is that psychosis and schizophrenia are diseases that typically strike people during adolescence or in their early 20s. But with increasing pot use, the number of people over 30 coming into the ER with psychosis has also shot up, suggesting that cannabis might be a cause of mental illness in people with no prior history of it.*”

That’s what the science would predict. Back in the early 1980s, Sven Andréasson, a Swedish doctor at the Karolinska Institute in Stockholm, launched one of the first big studies looking at the association between schizophrenia and marijuana. Andréasson was able to tap a huge database of information on Swedish men conscripted into military service, which included their drug-use history. He cross-referenced that data with national health service records to determine whether the 18- and 19-year-old men who’d used weed before 1970 had developed schizophrenia by 1983.

In a study published in The Lancet in 1987, he reported that for conscripts who had used weed more than 50 times, the risk of developing schizophrenia was six times as high as for those who’d never smoked. After adjusting for confounding factors, such as a family history of mental illness or existing symptoms of schizophrenia at the time of conscription, Andréasson found that using cannabis more than 10 times in adolescence more than doubled the risk of developing schizophrenia. Berenson quotes Andréasson as saying that if people used marijuana as much as they drank alcohol, “We would see an enormous amount of morbidity from cannabis.”

Today’s weed is insanely potent—products like “wax” and “shatter” come pretty close to 100 percent THC.

Before talking to Berenson, I didn’t realize it was possible to smoke your way to the ER. I smoked plenty of weed in high school and so did all my friends, and none of us jumped off a balcony or killed anyone—we could barely get off the couch. But the marijuana sold today is not what we smoked, which at 1 percent to 2 percent THC was the equivalent of smoking oregano. Today’s weed is insanely more potent, as are products like “wax” and “shatter”—forms of butane hash oil designed to be vaped or dabbed that come pretty close to 100 percent THC. And these high-potency products usually contain very little CBD oil, the ingredient in cannabis that’s supposed to account for many of its supposed health benefits.

These potent products can cause hallucinations, restlessness, and, as anyone who’s smoked even weak pot is familiar with, paranoia. After reading Berenson’s book, I fact-checked it a bit, and inadvertently discovered all sorts of websites advising pot users on how to manage their paranoia and ride out the psychotic effects. I also found plenty of news stories about bad trips on pot. Such incidents are typically treated jokingly. “But a lot of the time it turns out not to be a joke,” Berenson told me. “A lot of the time it’s a 22-year-old guy who maybe has some history of aggression, and he winds up throwing himself off the balcony or beating up his girlfriend.”

Paranoia and psychosis make people dangerous, so rising use of a drug that causes both would be expected to increase violent crime, rather than reduce it as pot advocates claim. Berenson looked at data for the four states that legalized weed in 2014 and 2015—Oregon, Washington, Alaska, and Colorado—and calculated a combined 35 percent increase in murders in those states from 2013 to 2017, compared with a 20-percent rise nationally. This “isn’t a statistical anomaly,” Berenson writes. “It’s real.”

The role of weed in rising violent crime rates in legalization states is a hotly contested question, especially in Colorado, where murders in Denver are at a 10-year high. Berenson admits he can’t say for sure whether those upswings are due to legal weed, but the raw data, he says, definitely contradicts advocates’ claims: “What I want people to stop saying is that legalization reduces violent crime. It doesn’t.”

Tell Your Children rounds out the crime stats with grisly stories of people who commit suicide or kill their children while high on pot, starting with the story of an Australian woman who, in the throes of cannabis-induced psychosis, stabbed eight kids to death—seven were hers. That’s a super-extreme case, but heinous crimes are not all that uncommon. Consider Texas: In 2017, Berenson told me, “2 percent of the state probably smokes marijuana every day, and 30 percent of the deaths from child abuse or neglect were committed while people were using. And that’s a bad number. There’s no way around it.”

“Maybe drugs are actually the problem,” Berenson says. “I feel like I’m going to get jumped on just for saying that.”

Once Berenson started looking into links between cannabis and violence or mental illness, he started to see them everywhere, and perhaps for good reason. The stories follow a familiar pattern: A guy—it’s frequently a guy—who smokes a lot of weed starts to go off the rails, ranting about politics or his ex, posting crazy shit on Facebook, and then ends up in the news for being suicidal, killing someone, or otherwise doing something crazy. Jared Loughner, the mass shooter who killed six people and wounded congresswoman Gabby Giffords in Arizona in 2011, was such a heavy pot user that the Army rejected him on that basis.

After reading Berenson’s book, I started seeing the patterns, too. In November, Jeffrey Clark, an alleged neo-Nazi, was arrested in DC for stockpiling weapons and making threats after the Pittsburgh synagogue mass shooting. His story fit the profile Berenson lays out in the book, so I checked: Indeed, court records suggest he was a pot addict. (Clark was charged with possession and distribution.)

And we’ve all heard about Kanye West’s and Saturday Night Live star Pete Davidson’s experiences. In an observation that’s likely to earn him even more derision than his suggestion that weed can cause violent crime, Berenson raises the possibility in the book that pot use might lie at the heart of both men’s mental health problems—West and Davidson have denied this—or at least that weed might be exacerbating their issues. (When I asked Berenson over the phone whether weed was really making Kanye crazy, several of my newsroom colleagues burst out laughing—an early sign of how this all might be received.)

Berenson notes in his book that West has acknowledged smoking before some of his most incomprehensible public appearances, and that the rapper’s insurer initially refused to cover his losses when West’s mental breakdown and psych hospitalization led to cancellation of a 2016 tour. The insurance company, Lloyd’s of London, argued in court documents that West’s marijuana use caused the breakdown and invalidated his insurance claim. (West sued the insurer, which eventually settled and paid most of the claims.) “I have no idea what goes on in that man’s head,” Berenson admits. But he doesn’t think it’s a coincidence that marijuana seems to be a factor when “these very high-profile figures are acting out in weird ways.”

Berenson suspects that the risks of marijuana may be, to the left, as the dangers of climate change are to the right.

Berenson is well aware that many people won’t want to hear his message, particularly on the left, at a time when prominent figures from presidential hopeful Sen. Cory Booker (D-N.J.) to Senate Minority Leader Chuck Schumer (D-N.Y.) have endorsed legalizing pot nationally. There’s a huge difference, he points out, between decriminalizing weed to fight mass incarceration and turning cannabis into a recreational drug as cheap and easy to obtain as booze. “If you look at what’s happened with opioids in the last 20 years, legalizers should be looking at that and saying to themselves, ‘Maybe drugs are actually the problem,’” Berenson says. “I feel like I’m going to get jumped on just for saying that.”

He finds something odd about the way Americans now view marijuana, as though it’s some sort of cool, harmless miracle drug—even though it has many of the same downsides alcohol does. A nice wine can complement a good meal. But in a different context, “alcohol can cause bar fights. It can cause drunken driving. It can cause domestic violence. It causes terrible violence,” he says. “Yet we’re able to sort of keep those two ideas in our head: that there’s one kind of alcohol consumption that can just put [people] to sleep, and there’s another kind that can cause violence. With marijuana, those two things are also true, but we’ve sort of forgotten the second thing exists.”

He suspects legalization is to the left what climate change is to the right—an issue around which even the most solid facts may not change minds. “I know I’m going to fail on this, but I really view this as a book about medicine and science,” he says. “This comes out of really smart people doing really careful research and trying to figure out how to tease out correlation and causation, and they got an answer. I believe the people I talk to. They don’t have any agenda other than trying to promote the public health.”

Correction: An earlier version of this article overstated the connection that NASEM researchers found between marijuana, bipolar disorder, and the risk of suicide, depression, and social anxiety disorders. It also overstated the connection between the increasing number of pot users and the number of people over 30 coming into the ER with psychosis; the researchers in that case “did not directly examine whether marijuana had led to any psychotic diagnoses.” A handful of other facts and statements in the piece have been updated for accuracy.