Addictions
Four new studies show link between heavy cannabis use, serious health risks
Cannabis products purchased in Ontario and B.C., including gummies, pre-rolled joints, chocolates and dried flower; April 11, 2025. [Photo credit: Alexandra Keeler]
By Alexandra Keeler
New Canadian research shows a connection between heavy cannabis use and dementia, heart attacks, schizophrenia and even death
Six months ago, doctors in Boston began noticing a concerning trend: young patients were showing up in emergency rooms with atypical symptoms and being diagnosed with heart attacks.
“The link between them was that they were heavy cannabis users,” Dr. Ahmed Mahmoud, a cardiovascular researcher and physician in Boston, told Canadian Affairs in an interview.
These frontline observations mirror emerging evidence by Canadian researchers showing heavy cannabis use is associated with significant adverse health impacts, including heart attacks, schizophrenia and dementia.
Sources warn public health measures are not keeping pace with rapid changes to cannabis products as the market is commercialized.
“The irony of this moment is that society’s risk perception of cannabis is at an all-time low, at the exact moment that the substance is probably having increasingly negative health impacts,” said Dr. Daniel Myran, a physician and Canada Research Chair at the University of Ottawa. Myran was lead researcher on three new Canadian studies on cannabis’ negative health impacts.
Legalization
Canada was the first G7 country to create a commercial cannabis market when it legalized the production and sale of cannabis in 2018.
The drug is now widely used in Canada.
In the 2024 Canadian Cannabis Survey, an annual government survey of cannabis trends, 26 per cent of respondents said they used cannabis for non-medical purposes in the past year, up from 22 per cent in 2018. Among youth, that number was 41 per cent.
Health Canada’s website warns that cannabis use can lower blood pressure and raise heart rates, which can increase the risk of a heart attack. But the warnings on cannabis product labels vary. Some mention risks of anxiety or effects on memory and concentration, but make no mention of cardiovascular risks.
The annual cannabis survey also shows a significant percentage of Canadians remain unaware of cannabis’ health risks.
In the survey, only 70 per cent of respondents said they had enough reliable information to make informed decisions about cannabis use. And 50 per cent of respondents said they had not seen any education campaigns or public health messages about cannabis.
At the same time, researchers are finding mounting evidence that cannabis use is associated with health risks.
A 2023 study by researchers at the University of Calgary, the University of Alberta and Alberta Health Services found that adults with cannabis use disorder faced a 60 per cent higher risk of experiencing adverse cardiovascular events — including heart attacks. Cannabis use disorder is marked by the inability to stop using cannabis despite negative consequences, such as work, social, legal or health issues.
Between February and April of this year, three other Canadian studies linked frequent cannabis use to elevated risks of developing schizophrenia, dementia and mortality. These studies were primarily conducted by researchers at the Ottawa Hospital Research Institute and ICES uOttawa (formerly the Institute for Clinical Evaluative Sciences).
“These results suggest that individuals who require hospital-based care for a [cannabis use disorder] may be at increased risk of premature death,” said the study linking cannabis-related hospital visits with increased mortality rates.
The three 2024 studies all examined the impacts of severe cannabis use, suggesting more moderate users may face lower risks. The researchers also cautioned that their research shows a correlation between heavy cannabis use and adverse health effects, but does not establish causality.
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Budtenders
Health experts say they are troubled by the widespread perception that cannabis is entirely benign.
“It has some benefits, it has some side effects,” said Mahmoud, the Boston cardiovascular researcher. “We need to raise awareness about the side effects as well as the benefits.”
Some also expressed concern that the commercialization of cannabis products in Canada has created a race to produce products with elevated levels of THC, the main psychoactive compound that produces a “high.”
THC levels have more than doubled since legalization, yet even products with high THC levels are marketed as harmless.
“The products that are on the market are evolving in ways that are concerning,” Myran said. “Higher THC products are associated with considerably more risk.”
Myran views cannabis decriminalization as a public health success, because it keeps young people out of the criminal justice system and reduces inequities faced by Indigenous and racialized groups.
“[But] I do not think that you need to create a commercial cannabis market or industry in order to achieve those public health benefits,” he said.
Since decriminalization, the provinces have taken different approaches to regulating cannabis. But even in provinces where governments control cannabis distribution, such as New Brunswick and Nova Scotia, products with high THC levels dominate retail shelves and online storefronts.
In Myran’s view, federal and provincial governments should instead be focused on curbing harmful use patterns, rather than promoting cannabis sales.
Ian Culbert, executive director of the Canadian Public Health Association, thinks governments’ financial interest in the cannabis industry creates a conflict of interest.
“[As with] all regulated substances, governments are addicted to the revenue they create,” he said. “But they also have a responsibility to safeguard the well-being of citizens.”
Culbert believes cannabis retailers should be required to educate customers about health risks — just as bartenders are required to undergo Smart Serve training and lottery corporations are required to mitigate risks of gambling addiction.
“Give ‘budtenders’ the training around potential health risks,” he said.
“While cannabis may not be the cause of some of these negative health events … it is the intersection at which an intervention can take place through the transaction of sales. So is there something we can do there that can change the trajectory of a person’s life?”
This article was produced through the Breaking Needles Fellowship Program, which provided a grant to Canadian Affairs, a digital media outlet, to fund journalism exploring addiction and crime in Canada. Articles produced through the Fellowship are co-published by Break The Needle and Canadian Affairs.
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From the Brownstone Institute
Cigarettes kill nearly half a million Americans each year. Everyone knows it, including the Food and Drug Administration. Yet while the most lethal nicotine product remains on sale in every gas station, the FDA continues to block or delay far safer alternatives.
Nicotine pouches—small, smokeless packets tucked under the lip—deliver nicotine without burning tobacco. They eliminate the tar, carbon monoxide, and carcinogens that make cigarettes so deadly. The logic of harm reduction couldn’t be clearer: if smokers can get nicotine without smoke, millions of lives could be saved.
Sweden has already proven the point. Through widespread use of snus and nicotine pouches, the country has cut daily smoking to about 5 percent, the lowest rate in Europe. Lung-cancer deaths are less than half the continental average. This “Swedish Experience” shows that when adults are given safer options, they switch voluntarily—no prohibition required.
In the United States, however, the FDA’s tobacco division has turned this logic on its head. Since Congress gave it sweeping authority in 2009, the agency has demanded that every new product undergo a Premarket Tobacco Product Application, or PMTA, proving it is “appropriate for the protection of public health.” That sounds reasonable until you see how the process works.
Manufacturers must spend millions on speculative modeling about how their products might affect every segment of society—smokers, nonsmokers, youth, and future generations—before they can even reach the market. Unsurprisingly, almost all PMTAs have been denied or shelved. Reduced-risk products sit in limbo while Marlboros and Newports remain untouched.
Only this January did the agency relent slightly, authorizing 20 ZYN nicotine-pouch products made by Swedish Match, now owned by Philip Morris. The FDA admitted the obvious: “The data show that these specific products are appropriate for the protection of public health.” The toxic-chemical levels were far lower than in cigarettes, and adult smokers were more likely to switch than teens were to start.
The decision should have been a turning point. Instead, it exposed the double standard. Other pouch makers—especially smaller firms from Sweden and the US, such as NOAT—remain locked out of the legal market even when their products meet the same technical standards.
The FDA’s inaction has created a black market dominated by unregulated imports, many from China. According to my own research, roughly 85 percent of pouches now sold in convenience stores are technically illegal.
The agency claims that this heavy-handed approach protects kids. But youth pouch use in the US remains very low—about 1.5 percent of high-school students according to the latest National Youth Tobacco Survey—while nearly 30 million American adults still smoke. Denying safer products to millions of addicted adults because a tiny fraction of teens might experiment is the opposite of public-health logic.
There’s a better path. The FDA should base its decisions on science, not fear. If a product dramatically reduces exposure to harmful chemicals, meets strict packaging and marketing standards, and enforces Tobacco 21 age verification, it should be allowed on the market. Population-level effects can be monitored afterward through real-world data on switching and youth use. That’s how drug and vaccine regulation already works.
Sweden’s evidence shows the results of a pragmatic approach: a near-smoke-free society achieved through consumer choice, not coercion. The FDA’s own approval of ZYN proves that such products can meet its legal standard for protecting public health. The next step is consistency—apply the same rules to everyone.
Combustion, not nicotine, is the killer. Until the FDA acts on that simple truth, it will keep protecting the cigarette industry it was supposed to regulate.
Author
By Adam Zivo
Both are shaped by radical LGBTQ activism and questionable evidence.
Over the past decade, North America embraced two disastrous public health movements: pediatric gender medicine and “harm reduction” for drug use. Though seemingly unrelated, these movements are actually ideological siblings. Both were profoundly shaped by extremist LGBTQ activism, and both have produced grievous harms by prioritizing ideology over high-quality scientific evidence.
While harm reductionists are known today for championing interventions that supposedly minimize the negative effects of drug consumption, their movement has always been connected to radical “queer” activism. This alliance began during the 1980s AIDS crisis, when some LGBTQ activists, hoping to reduce HIV infections, partnered with addicts and drug-reform advocates to run underground needle exchanges.
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In the early 2000s, after the North American AIDS epidemic was brought under control, many HIV organizations maintained their relevance (and funding) by pivoting to addiction issues. Despite having no background in addiction medicine, their experience with drug users in the context of infectious diseases helped them position themselves as domain experts.
These organizations tended to conceptualize addiction as an incurable infection—akin to AIDS or Hepatitis C—and as a permanent disability. They were heavily staffed by progressives who, influenced by radical theory, saw addicts as a persecuted minority group. According to them, drug use itself was not the real problem—only society’s “moralizing” norms.
These factors drove many HIV organizations to lobby aggressively for harm reduction at the expense of recovery-oriented care. Their efforts proved highly successful in Canada, where I am based, as HIV researchers were a driving force behind the implementation of supervised consumption sites and “safer supply” (free, government-supplied recreational drugs for addicts).
From the 2010s onward, the association between harm reductionism and queer radicalism only strengthened, thanks to the popularization of “intersectional” social justice activism that emphasized overlapping forms of societal oppression. Progressive advocates demanded that “marginalized” groups, including drug addicts and the LGBTQ community, show enthusiastic solidarity with one another.
These two activist camps sometimes worked on the same issues. For example, the gay community is struggling with a silent epidemic of “chemsex” (a dangerous combination of drugs and anonymous sex), which harm reductionists and queer theorists collaboratively whitewash as a “life-affirming cultural practice” that fosters “belonging.”
For the most part, though, the alliance has been characterized by shared tones and tactics—and bad epistemology. Both groups deploy politicized, low-quality research produced by ideologically driven activist-researchers. The “evidence-base” for pediatric gender medicine, for example, consists of a large number of methodologically weak studies. These often use small, non-representative samples to justify specious claims about positive outcomes. Similarly, harm reduction researchers regularly conduct semi-structured interviews with small groups of drug users. Ignoring obvious limitations, they treat this testimony as objective evidence that pro-drug policies work or are desirable.
Gender clinicians and harm reductionists are also averse to politically inconvenient data. Gender clinicians have failed to track long-term patient outcomes for medically transitioned children. In some cases, they have shunned detransitioners and excluded them from their research. Harm reductionists have conspicuously ignored the input of former addicts, who generally oppose laissez-faire drug policies, and of non-addict community members who live near harm-reduction sites.
Both fields have inflated the benefits of their interventions while concealing grievous harms. Many vulnerable children, whose gender dysphoria otherwise might have resolved naturally, were chemically castrated and given unnecessary surgeries. In parallel, supervised consumption sites and “safer supply” entrenched addiction, normalized public drug use, flooded communities with opioids, and worsened public disorder—all without saving lives.
In both domains, some experts warned about poor research practices and unmeasured harms but were silenced by activists and ideologically captured institutions. In 2015, one of Canada’s leading sexologists, Kenneth Zucker, was fired from the gender clinic he had led for decades because he opposed automatically affirming young trans-identifying patients. Analogously, dozens of Canadian health-care professionals have told me that they feared publicly criticizing aspects of the harm-reduction movement. They thought doing so could invite activist harassment while jeopardizing their jobs and grants.
By bullying critics into silence, radical activists manufactured false consensus around their projects. The harm reductionists insist, against the evidence, that safer supply saves lives. Their idea of “evidence-based policymaking” amounts to giving addicts whatever they ask for. “The science is settled!” shout the supporters of pediatric gender medicine, though several systematic reviews proved it was not.
Both movements have faced a backlash in recent years. Jurisdictions throughout the world are, thankfully, curtailing irreversible medical procedures for gender-confused youth and shifting toward a psychotherapy-based “wait and see” approach. Drug decriminalization and safer supply are mostly dead in North America and have been increasingly disavowed by once-supportive political leaders.
Harm reductionists and queer activists are trying to salvage their broken experiments, occasionally by drawing explicit parallels between their twin movements. A 2025 paper published in the International Journal of Drug Policy, for example, asserts that “efforts to control, repress, and punish drug use and queer and trans existence are rising as right-wing extremism becomes increasingly mainstream.” As such, there is an urgent need to “cultivate shared solidarity and action . . . whether by attending protests, contacting elected officials, or vocally defending these groups in hostile spaces.”
How should critics respond? They should agree with their opponents that these two radical movements are linked—and emphasize that this is, in fact, a bad thing. Large swathes of the public understand that chemically and surgically altering vulnerable children is harmful, and that addicts shouldn’t be allowed to commandeer public spaces. Helping more people grasp why these phenomena arose concurrently could help consolidate public support for reform and facilitate a return to more restrained policies.
Adam Zivo is director of the Canadian Centre for Responsible Drug Policy.
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