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Four new studies show link between heavy cannabis use, serious health risks

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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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News For Those Who Think Drug Criminalization Is Racist. Minorities Disagree

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A Canadian poll finds that racial minorities don’t believe drug enforcement is bigoted.

By Adam Zivo

[This article was originally published in City Journal, a public policy magazine and website published by the Manhattan Institute for Policy Research]

Is drug prohibition racist? Many left-wing institutions seem to think so. But their argument is historically illiterate—and it contradicts recent polling data, too, which show that minorities overwhelmingly reject that view.

Policies and laws are tools to establish order. Like any tool, they can be abused. The first drug laws in North America, dating back to the late nineteenth and early twentieth centuries, arguably fixated on opium as a legal pretext to harass Asian immigrants, for example. But no reasonable person would argue that laws against home invasion, murder, or theft are “racist” because they have been misapplied in past cases. Absent supporting evidence, leaping from “this tool is sometimes used in racist ways” to “this tool is essentially racist” is kindergarten-level reasoning.

Yet this is precisely what institutions and activist groups throughout the Western world have done. The Drug Policy Alliance, a U.S.-based organization, suggests that drug prohibition is rooted in “racism and fear.” Harm Reduction International, a British NGO, argues for legalization on the grounds that drug prohibition entrenches “racialized hierarchies, which were established under colonial control and continue to dominate today.” In Canada, where I live, the top public health official in British Columbia, our most drug-permissive province, released a pro-legalization report last summer claiming that prohibition is “based on a history of racism, white supremacy, paternalism, colonialism, classism and human rights violations.”

These claims ignore how drug prohibition has been and remains popular in many non-European societies. Sharia law has banned the use of mind-altering substances since the seventh century. When Indigenous leaders negotiated treaties with Canadian colonists in the late 1800s, they asked for “the exclusion of fire water (whiskey)” from their communities. That same century, China’s Qing Empire banned opium amid a national addiction crisis. “Opium is a poison, undermining our good customs and morality,” the Daoguang emperor wrote in an 1810 edict.

Today, Asian and Muslim jurisdictions impose much stiffer penalties on drug offenders than do Western nations. In countries like China, Saudi Arabia, Iran, Singapore, and Thailand, addicts and traffickers are given lengthy prison sentences or executed. Meantime, in Canada and the United States, de facto decriminalization has left urban cores littered with syringes and shrouded in clouds of meth.

The anti-drug backlash building in North America appears to be spearheaded by racial minorities. When Chesa Boudin, San Francisco’s former district attorney, was recalled in 2022, support for his ouster was highest among Asian voters. Last fall, 73 percent of Latinos backed California’s Proposition 36, which heightened penalties for drug crimes, while only 58 percent of white respondents did.

In Canada, the first signs of a parallel trend emerged during Vancouver’s 2022 municipal election, where an apparent surge in Chinese Canadian support helped install a slate of pro-police candidates. Then, in British Columbia’s provincial election last autumn, nonwhite voters strongly preferred the BC Conservatives, who campaigned on stricter drug laws. And in last month’s federal election, within both Vancouver and Toronto’s metropolitan areas, tough-on-crime conservatives received considerable support from South Asian communities.

These are all strong indicators that racial minorities do not, in fact, universally favor drug legalization. But their small population share means there is relatively little polling data to measure their preferences. Since only 7.6 percent of Americans are Asian, for example, a poll of 1,000 randomly selected people will yield an average of only 76 Asian respondents—too small a sample from which to draw meaningful conclusions. You can overcome this barrier by commissioning very large polls, but that’s expensive.

Nonetheless, last autumn, the Centre for Responsible Drug Policy (a nonprofit I founded and operate) did just that. In partnership with the Macdonald-Laurier Institute, we contracted Mainstreet Research to ask over 12,000 British Columbians: “Do you agree or disagree that criminalizing drugs is racist?”

The results undermine progressives’ assumptions. Only 26 percent of nonwhite respondents agreed (either strongly or weakly) that drug criminalization is racist, while over twice as many (56 percent) disagreed. The share of nonwhite respondents who strongly disagreed was three times larger than the share that strongly agreed (43.2 percent versus 14.3 percent). These results are fairly conclusive for this jurisdiction, given the poll’s sample size of 2,233 nonwhite respondents and a margin of error of 2 percent.

Notably, Indigenous respondents seemed to be the most anti-drug ethnic group: only 20 percent agreed (weakly or strongly) with the “criminalization is racist” narrative, while 61 percent disagreed. Once again, those who disagreed were much more vehement than those who agreed. With a sample size of 399 respondents, the margin of error here (5 percent) is too small to confound these dramatic results.

We saw similar outcomes for other minority groups, such as South Asians, Southeast Asians, Latinos, and blacks. While Middle Eastern respondents also seemed to follow this trend, the poll included too few of them to draw definitive conclusions. Only East Asians were divided on the issue, though a clear majority still disagreed that criminalization is racist.

As this poll was limited to British Columbian respondents, our findings cannot necessarily be assumed to hold throughout Canada and the United States. But since the province is arguably the most drug-permissive jurisdiction within the two countries, these results could represent the ceiling of pro-drug, anti-criminalization attitudes among minority communities.

Legalization proponents and their progressive allies take pride in being “anti-racist.” Our polling, however, suggests that they are not listening to the communities they profess to care about.

 

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Why the U.S. Shouldn’t Copy Canada’s Experiment with Free Drugs

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By Adam Zivo

Harm-reduction activists claim evidence supports “safer supply,” but their studies don’t back that up.

Canada, where I call home, is the only jurisdiction in the world that hands out free addictive drugs to addicts. Under the “safer-supply” policy, Canadian health authorities distribute hydromorphone—an opioid as potent as heroin—as well as, to a lesser degree, oxycodone, pharmaceutical fentanyl, and mild stimulants. These drugs are provided at no cost and, until recently, rarely had to be consumed under medical supervision.

Some American harm-reduction activists claim that Canada’s experience—and studies of it—prove that safer supply saves lives. In reality, the studies they cite are deeply flawed. They rely on weak methodologies, including biased interviews and self-reported surveys, and fail to isolate the effects of safer supply from those of other interventions. U.S. policymakers should not let such shaky evidence justify similarly misguided policies at home.

Canada piloted safer supply in 2016 with no evidence that it worked. Some clinical trials suggested that administering pharmaceutical-grade heroin under careful medical supervision could stabilize severely addicted drug users. But advocates took this evidence and claimed that it supported their safer-supply experiment, despite crucial dissimilarities—the most important being the lack of witnessed consumption.

Over the following years, radical activist-scholars produced numerous evaluations and studies declaring that safer supply “saves lives” and improves recipients’ quality of life. As Canada expanded program access nationwide in 2020, policymakers latched on to this “evidence-based” experiment, condemning critics as anti-science.

This evidence is predominantly composed of qualitative studies, which rely not on data but on interviews with safer-supply recipients and providers. The interviewees naturally say that the program is wonderful and has few downsides. Advocates then frame these responses as objective evidence of success.

Notably, the studies never reach out to those who might provide negative evaluations of safer supply—doctors, addicts uninvolved with these programs, or individuals newly in recovery. Addiction experts throughout Canada have dismissed these studies as glorified customer testimonials.

Some studies involve surveys, converting patient responses into quantitative data that can be statistically analyzed. For example, the London InterCommunity Health Centre (LIHC), one of Canada’s leading safer-supply prescribers, publishes survey-based evaluations that claim approximately half of its patients reduced their fentanyl consumption after enrollment. This quantitative method does not change the unreliability of self-reported data, however, and there’s nothing that keeps patients from giving false answers if it suits their interests.

2024 study conducted by Brian Conway, director of Vancouver’s Infectious Disease Centre, indirectly validated these criticisms. The study distributed surveys to 50 of his safer-supply patients and then collected urine samples immediately afterward. Conway discovered that, while only 4 percent of these patients self-reported diverting (selling or trading) all their safer-supply hydromorphone, 24 percent had no hydromorphone in their urine. That suggests a significant portion of patients lied on their surveys.

A few studies use administrative health data to show that enrollment in federally funded safer-supply programs correlates with improved health outcomes. But these studies make no effort to determine whether the free drugs themselves are responsible. The real driver could be the extensive wraparound services the programs offer, such as housing assistance and access to primary care. It’s like giving an obese man a personal trainer and a daily slice of cake—and then, when he loses weight, crediting the cake.

Last year, the British Columbia Centre for Disease Control (BCCDC) published a study in the British Medical Journal examining the health data of 5,882 drug users over an 18-month period between 2020 and 2021. The study found that individuals who received safer-supply opioids were 61 percent less likely to die over the following week than those who didn’t. This number rose to 91 percent for those receiving safer-supply opioids for four or more days in a single week.

Encouraging, right? But not so fast. When a team of seven addiction physicians reviewed the study, they discovered that the researchers misrepresented their data. Safer-supply patients are often co-prescribed traditional addiction medications, such as methadone and Suboxone, that have long been proven to reduce overdoses and deaths (these medications are often referred to as opioid agonist therapy, or OAT). The study data showed that safer-supply patients who did not also receive OAT medications were just as likely to die as those who did not get safer supply. In other words, the benefits that the BCCDC researchers touted were likely driven primarily by OAT, not safer supply.

The study data also showed no significant mortality reductions after one year of accessing safer supply. One wonders why the researchers chose to fixate on the one-week follow-up numbers.

Most recently, a study published in JAMA Health Forum found that, between 2020 and 2022, British Columbia’s safer-supply policy was associated with a 33 percent increase in opioid hospitalizations and no change to drug-related mortality. The researchers arrived at this conclusion by comparing the province’s publicly available health data with data from a control group made up of a handful of other Canadian provinces. The study raised further doubts about safer supply’s scientific basis.

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Over the past two years, Canadian policymakers have openly, if reluctantly, acknowledged that safer supply is not as well-supported as they once claimed. British Columbia’s 2023 safer supply fentanyl protocols clearly state, for example, that “there is no evidence available supporting this intervention, safety data, or established best practices for when and how to provide it.” Similarly, the province’s top doctor released a report in early 2024 admitting that the experiment is “not fully evidence based.” Just last autumn, the Canadian Research Initiative in Substance Matters acknowledged in a major presentation that safer supply is supported by “essentially low-level evidence.”

This about-face has been hastened by investigative media reports confirming that safer-supply drugs were being diverted to the black market, enriching organized crime and corrupt pharmacies in the process. Public support for the policy has apparently declined, as once-taboo criticism becomes normalized among Canadian politicians and commentators. The Canadian federal government has now quietly defunded its safer-supply programs (though independent prescribers still operate), while British Columbia mandated earlier this year that all safer-supply drugs be consumed under supervision.

Harm-reduction activists nonetheless maintain that the blowback against safer supply represents a “moral panic,” and that politics is overriding evidence-based policymaking. “Safer supply saves lives! Follow the science!” they insist. International policymakers, especially in the United States, should see through these misrepresentations.

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