Cannabis and the adolescent brain: What science knows, and doesn’t know

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On the April morning of 4/20, the “weed holiday” when crowds toke up in public places, Nick wrote a Grade 12 history test on the French Revolution while stoned: “I got an 82,” he says, “which is a pretty good mark.”

He’s offering this detail as evidence that, after three years of experimenting with pot in high school, his memory is intact, his brain is not fried, the life-destroying danger warned of in drug-education assemblies has not, in his experience, come true.

On a Sunday afternoon of the May long weekend, with his parents away, he’s been playing the video game Fortnite in his Toronto-area bedroom, listening to the rapper Rich the Kid, and now, on his smartphone, he’s making the case for why he thinks the adults need to chill out about marijuana. He smoked a joint an hour before the interview, which might explain the mellow amble into the merits of Fortnite. Otherwise, given his rapid-fire recall of pot research, it’s hard to tell.

“Did you know,” he asks, “that you’d have to smoke 1,500 pounds of marijuana for like, 30 minutes, to die? That’s physically impossible.” (I check: He’s quoting a 1988 ruling from the U.S. Drug Enforcement Administration, almost verbatim: The time stated is actually 15 minutes.) Yeah, he says, “I’ve done a lot of reading.”

Nick would prefer his last name not be used – he doesn’t advertise his pot smoking to his parents. When we first spoke a couple of years ago, Nick was conducting his own single-subject marijuana trial. If he binged for a few days, he’d take a week or two off. “To make sure I don’t go overboard,” he said then. Now, in his last semester of high school, he’s smoking more than ever – three or four times a week, mostly on weekends. “I’ve been paying close attention to see if there are any faults in my memory, and the truth is I haven’t seen any.”

In fact, he says, he’s getting the best grades of his high-school career. He’s made the honour roll. Until recently, he was swimming competitively. He’s holding down a part-time job. And he was accepted into both his top choices for university.

As one scientist observed, Nick might be doing even better if he weren’t getting high so often. But for a teenager with a relatively heavy drug habit, he comes across as a successful, functional 17-year-old.

And when it comes to pot research, he’s still a puzzle.

Last year, a committee of experts for the National Academies of Sciences, Engineering, and Medicine in the United States released a detailed analysis of the published studies on marijuana. They looked at more than 10,000 papers, selected the ones they deemed to be of highest quality, and assessed the strength of the science. The report is 500 pages of carefully fudged conclusions that highlight the gaping holes in cannabis research. For instance: Does pot cause lung cancer? “There is moderate evidence of no statistical association,” the reports says. Does it make you more likely to die prematurely, or from an overdose? “There is no or insufficient evidence to refute or support a statistical association.” On the possible long-term consequences that cause parents the most worry – pot’s association with psychosis, brain damage and addiction – the report also offers more caveats than conclusions.

The studies that have rolled out since have been equally confounding. A meta-analysis published in April in JAMA Psychiatry, for example, found that once teenaged pot users went off the drug – even for as little as 72 hours – their scores on cognitive tests were not significantly different from non-drug users.

Other studies have also found the “stoner” deficit to be temporary. Scientists believe that the adolescent brain is at higher risk because it’s developing rapidly in the same areas affected by the “high” from pot. But brain scans showing structural changes are often based on smaller samples of chronic, frequent users. Since they don’t have a before-picture of those same brains, researchers can’t say for certain whether marijuana is the cause, or a consequence that happens along the way. James MacKillop, co-director of the Michael G. DeGroote Centre for Medicinal Cannabis Research at McMaster University, compares the problem to a crime-scene photograph. “Pot may be present, but is it the culprit?”

One issue is that the subjects in studies tend to be people using a lot of marijuana for a long time. But it’s much more common for teenagers to dabble in pot for a while, and wean themselves when adult responsibilities arrive. And researchers know even less about this second group.

As Canada heads into its own real-world pot experiment, the best they can say is that cannabis will likely turn out to be neither devastating for most teens, nor benign for all of them.

In other words, most Nicks will probably end up just fine.

But not everyone is a Nick.

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The cautionary tale

A week before Nick’s pot-hazed history exam, Jonathan Kropman, 23, went to rehab. Driving to a treatment facility in Port Hope, Ont., run by the Canadian Centre for Addictions, he made his father stop five times so he could smoke pot on the side of the road. At the centre, he reluctantly parted with his last three joints, after his dad persuaded him not to sneak them in.

It was a long journey to this point. In the spring, Mr. Kropman flew home a week early from a Mexican vacation with his family – booking the flight without his parents’ knowledge – because he felt he couldn’t go another seven days without pot. The previous April, he had woken up in a jail cell at Toronto’s Old City Hall with a foggy memory of the night before. He needed to be told that, while intoxicated and smoking weed at the corner of Yonge and Dundas, he’d swung a punch at the police officer who stopped to question him. This wasn’t his first pot-induced trouble – in Grade 8, he was suspended from school for possessing a joint. But it was adding up: “I really have to change my life,” he decided. For one thing, he said later, from rehab, “no woman is going to want to be with an addict.”

Mr. Kropman took his first haul on a joint in a playground after school in Grade 6, when he was 11 years old. This alone makes him an outlier: According to a 2017 Ontario student drug survey, only about 2 per cent of teens have tried pot by Grade 8, a number that rises to 37 per cent in Grade 12. But Mr. Kropman played sports with older kids, and weed was always around. “It was the cool thing to hang out with the bad crowd. I didn’t know what I was getting into,” he recalls. “From the first toke, I knew – I was addicted to the feeling. It was euphoric, an escape.”

Even before then, Mr. Kropman says he was “definitely a trouble-maker” and a risk-taker. He was sent home in Grade 4 for fighting in school. He had a special worker who sat with him in class to help him with work and monitor his behaviour. By junior high, he was using pot all the time, and drinking as well, although he preferred weed to alcohol. Pot, he explains, “is a lot easier to hide. You just put [eye drops] in your eyes.”

The warnings that he was causing damage to his brain, he says, “went in one ear and out the other.” His mother was firm: She didn’t want him using. His father was less strict – growing up, Mr. Kropman says, his dad also smoked a lot of weed. As they became more aware of his habit, they tried to talk him into cutting back: “I wasn’t listening.”

Instead, his drug use escalated – he got weed from friends with medical marijuana licences and, eventually, his own prescription, he says, given to him for help with sleeping. He couldn’t cope without a ready supply. Working construction, after high school, he smoked weed to stay focused during the tedium of painting houses. Eventually, he was drinking, smoking and, finally, using cocaine, which he tried one night when he was stumbling drunk. (Pot’s reputation as a gateway drug was also cast into doubt by the National Academies report, which stated that the examined studies “did not provide compelling evidence.”) Mr. Kropman insists it was alcohol – not cannabis – that paved his path to the hard stuff; stoned, he says, he would have been too nervous to try it.

At the time we speak, Mr. Kropman had completed more than a month of treatment, cold turkey. “This place definitely saved my life.” The physical cravings are gone, he explained, but the mental struggle is just beginning. “I still crave it, absolutely.” On a Saturday in May, he left rehab for a sober-living house, where he can stay for three months as long as he passes regular drug tests. As of this Thursday, he’s been “clean and sober” for 78 days. “I am going to give it my best shot.”

Of all the pot-induced problems that adults worry about, addiction should be at the top of the list, says Jean-Sébastien Fallu, a psychologist at the University of Montreal who has edited a book on cannabis research coming out this fall. About 9 per cent of adults who start smoking pot will become addicted, Mr. Fallu says. Among teenagers, he says, the rate is 16 per cent – and nine times more likely, for instance, than the risk of a pot-smoking teenager developing schizophrenia.

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Detective work

So why is Nick on the honour roll, and Jonathan going through rehab?

That’s the real detective work required to unravel the role that pot plays in Mr. MacKillop’s crime-scene photo. Are teens who start using cannabis at young ages different from their peers? How much do certain risk factors matter – an impulsive personality, a deviant peer group, childhood trauma – and in what combination? Is pot a supporting character in a tale of unfortunate events, or the villain that turns the tide?

Risk factors appear to be at least a partial explanation for many of the problems associated with cannabis. Teenagers who begin using early, and increase their use over time – as Mr. Kropman did – are more likely to become addicted; having a history of addiction in the family is also a contributing factor.

In some studies, accounting for risk factors significantly reduces – and even eliminates – the negative consequences associated with cannabis. A 2012 longitudinal study – one of the most well-regarded cannabis studies, and hence often cited as proof of the drug’s negative side effects – found that IQ fell among long-term, heavy users. But twin studies that compared pot-using teens with their non-using siblings didn’t find cognitive differences. When researchers adjust for criteria such as family background, parental education, intelligence and personality, the link between negative consequences, such as high-school dropouts and poor grades, often collapses. How often teenagers use pot also appears to be important: a June 2017 study found that young people who used twice a week or less performed as well as – and even slightly better – than non-users on tests measuring memory and executive control. And the National Academies report found “limited to no evidence” that, once people stopped using marijuana, there were sustained effects on learning, memory or attention.

“There is a nuance to the findings that need to be appreciated,” says Cobb Scott, a psychology professor at the University of Pennsylvania and lead author of the June 2017 study, who studies the effect of dose and abstinence on cognitive skills. “Our research suggests that these effects may be smaller than people were worried about and it’s possible they don’t reflect long-term damage to brain networks that support cognitive functioning.”

If damage does occur, however, the research suggests that early exposure is likely a key factor. A University of Montreal study published last December that tracked boys in Montreal from age six into their 30s found that, among those who smoked pot after age 17, there was no overall difference in cognitive skills – intelligence, executive function, decision-making – compared with their peers who hadn’t smoked. Those boys who started using cannabis before age 14 performed more poorly, especially in verbal cognitive tests. But even so, says Natalie Castellanos-Ryan, a psychology professor who co-authored the Montreal study, “we can’t assume it is the toxic effect of cannabis.” In many cases, other high risk factors were also present before marijuana, including poor grades and delinquent behaviour.

And even when studies do find a statistically significant negative association with cannabis use, Ms. Castellanos-Ryan says that the actual effect on an individual’s life may be small. Bottom line, she concludes: “There is a lot of missing research, and many of us are trying to fill in the gaps.”

One area where the science appears to be closer to an answer is the association between cannabis and schizophrenia. Rather than cause the serious mental illness, Ms. Castellanos-Ryan says, current research suggests that marijuana works as “a trigger” for young people already predisposed to psychosis. (In one study of pot users, for example, only those with a family history of schizophrenia developed the disease.)

It is still not clear whether not using cannabis would have prevented the disease in high-risk individuals. But those teenaged exposures appear to be key: Steven Laviolette, a biologist at the University of Western Ontario, says that while dosing juvenile rats with THC produces memory issues and psychotic behaviour, those changes are not seen in adult rats given the same dose.

Since schizophrenia develops during adolescence, and teenagers may not know their family history or whether they have a genetic sensitivity, Mr. Laviolette says it’s another argument for waiting until adulthood to use cannabis. “We haven’t figured it out yet,” he said. “But we can conclusively say it is a risky thing to do.”

Pot smokers are complicated study subjects – many of the same teens also drink alcohol and smoke cigarettes, both of which may bring even more significant harms than cannabis. (The National Academies report, for instance, found stronger evidence for tobacco as the first gateway drug than pot.) Comparisons between studies are tricky, since researchers may not ask about the same risk factors, or record data the same way.

Most studies also rely on self-reports, which aren’t particularly reliable, even for subjects not doing drugs. Aside from being present in real time, researchers can’t determine the potency of pot being ingested, or precisely how much.

Yet, one of the most important outstanding questions is whether stronger versions of cannabis – as well as different ways of using it – will produce different levels of harm. Today’s street pot is not Woodstock weed. The amount of THC, the mind-altering chemical in marijuana, has roughly tripled since the 1970s, and new concentrated versions, known by names such as shatter, wax and budder, may be 80-per-cent THC, or more than six times the level of the modern-day plant version.

“We certainly do not have strong evidence that low frequency use is associated with a lot of negative outcomes,” says Mr. MacKillop of the DeGroote Centre . But at the same time, he adds: “What was somewhat a murky science to start with is already playing catch-up to the brave new world of cannabis consumption.”

Science may eventually conclude that what makes some teenagers more susceptible to negative outcomes when they use cannabis is a complicated mix of interwoven conditions and life circumstances, both inherited and acquired.

“That is not an unlikely scenario,” says Susan Weiss, a researcher at the National Institute on Drug Abuse in the United States. “But it doesn’t mean that cannabis isn’t adding to the problem.”

Ms. Weiss is part of a groundbreaking, new study trying to get closer to the answer by following more than 10,000 American nine- and 10-year-olds through their teenage years, using regular cognitive tests, psychosocial surveys and brain scans to capture a before-and-after picture of drug use. But it won’t have findings for many years, long after pot is legal in Canada.

So while scientists are figuring things out, how do Canadian parents talk so their teens will listen?

Cannabis legalization is coming to Canada on Oct. 17. How will it work where you live?

Get caught up on what governments are doing to prepare for legal cannabis.

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High on the honour roll

“I figure live fast, die young,” explained Alex, a 17-year-old in St. Catharines, Ont., who smokes pot, he says, five or six times a week but, as with Nick, can also boast about being on the honour roll, with a university acceptance letter.

When it comes to the risk of marijuana, he says, “I worry about it the same way that you worry about eating at McDonald’s. It might give you a heart attack or make you fat, but people eat at McDonald’s all the time because it tastes so good.”

Would Alex really want to eat Big Macs every day? “No, probably not,” he admits. But it’s not a bad analogy. Even with the science still to be determined, the researchers interviewed for this story were unanimous in their best advice: Teenagers should wait until their brains are more developed (ideally, age 25), use infrequently, take breaks and avoid weed with high levels of THC. Adolescents with known risk factors – such as a history of schizophrenia or addiction in the family – should take special care. At the very least, like fast food, marijuana is safest consumed in small, spare doses. In the best-case scenario, researchers agreed, teenagers would never use pot.

On the positive side, says Mr. Fallu in Montreal, the fear that legalization will launch a tsunami of teenaged potheads has been grossly overstated, according to existing research. That’s not happened to date in states such as Washington and Colorado, where recreational cannabis has already been legalized.

In a 2017 Ontario student drug survey of more than 11,000 teens, 10 per cent of high-school students said they intended to try pot after it was legalized, and 4.9 per cent said they planned to use more often. By comparison, 53 per cent said they didn’t plan to use it either way.

Canadian teens already use pot at relatively high rates – a 2014 report by the World Health Organization placed Canada second behind France for 15-year-olds who said they’d used pot in the past 30 days. (Unlike many other countries, girls use at roughly the same rates as boys.) But the Ontario student study also found that overall drug use among teenagers – including cannabis – was the lowest recorded since the survey began in 1977, especially among younger grades.

And it’s not as if weed is hard to find now, as even teenagers not using pot told The Globe and Mail. Ellen, an Alberta high-school student, said she’d only have to wander across the street at lunch hour to the stoner kids smoking outside the 7-Eleven.

As legalization approaches, researchers such as Jean-Sébastien Fallu are calling for balance, so adults don’t discredit themselves with teenagers, who check everything on Google anyway. It is particularly frustrating, Mr. Fallu says, that parents often exaggerate the risks of cannabis, while minimizing the danger of alcohol, even though there’s research to suggest that binge drinking, in particular, may be even more harmful to physical health and the teenage brain.

Mr. Fallu suggests that a rational, science-based message about cannabis should present the risks, admit what is yet unknown and make clear that using drugs when you’re young is a gamble with potentially high stakes.

“Human beings want to have black-and-white facts, but the truth is rarely that clear, and not just in drug use,” he says. “There is uncertainty, but we can educate around that.”

Nine things you can say to your teen about cannabis and its risks

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1. There is a lot scientists don’t know. But researchers believe that starting before age 15 and using heavily through your teenage years is associated with the highest risk of harm. The government is legalizing marijuana not because it is completely safe but to regulate it and, ideally, make the street version of the drug less available to young people.

2. If you are going to use, take breaks. Pot may not be as addictive as other drugs, but the risk of addiction is still higher for teenagers. Taking a break is also good for your developing brain (and your lungs), and a way to see how marijuana might be negatively affecting your life and your relationships.

3. Just like alcohol, there are different potencies of pot. Again, it’s not certain, but the science suggests that higher levels of THC, the mind-altering chemical in the drug, may cause more damage to a young brain. The highest level of THC – as high as 80 per cent –is found in butane hash oil extractions, called shatter, wax or budder.

4. Be careful with edibles, which are the main cause of emergency-room visits for pot. All the THC in that pot brownie will be absorbed into your body. And the effect takes longer, so people may take too much before they realize it.

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5. Marijuana may not cause schizophrenia but scientists believe it is a potential trigger for teens with risk factors, such as family history. If you have a severe reaction to pot – hallucinations, for instance, or frightening paranoia – that may be a warning sign.

6. Some scientists will say that alcohol is worse than cannabis. But the harms of each drug are different. Using any drug when you’re young is more risky than when you’re an adult. Using them together appears to increase those risks.

7. Don’t drive if you have used marijuana, especially if you have been drinking too. Some people may say they drive better stoned, but research suggests otherwise – when people are high they react more slowly and think less clearly. Researchers who analyzed the existing data found a higher risk of car accidents when people drove while stoned.

8. Be skeptical of any headline that suggests a study has found the answer. Science gets misused on both sides, and legalization has also given cannabis companies a vested interest in overselling the drug’s positive effects.

9. Studies usually group a lot of people together to produce average findings. How each individual reacts to marijuana may be very different. But one thing is true for everyone: Your brain is developing until about age 25. Just like getting good sleep and eating well, avoiding alcohol and marijuana as much and for as long as possible helps ensure you’ll get the best one you can.

– Erin Anderssen