By Alexandra Keeler

Experts warn surging THC levels are fuelling growing health risks — and say stronger regulation is urgently needed

More and more cannabis users are ending up in emergency rooms suffering from severe, repeated bouts of vomiting — a condition known as cannabis hyperemesis syndrome.

A new study found that emergency visits for cannabis hyperemesis syndrome increased 13-fold over eight years, accounting for more than 8,000 of the nearly 13,000 cannabis-related ER visits in that period.

Experts say the mounting health risks associated with cannabis use are due to rising THC levels in cannabis products. They urge stronger regulation, better labeling and more research — using Quebec’s approach as a potential model.

“I don’t think we have the perfect model in Quebec — there’s pros and cons,” said Dr. Didier Jutras-Aswad, a clinical scientist at the Centre hospitalier de l’Université de Montréal (CHUM) and a professor in the Department of Psychiatry and Addiction at Université de Montréal.

“But overall, the process of … progressively implementing changes, not wanting to be the first one in line to put all this new product on the market, I think is probably, in terms of public health, more prudent.”

THC levels

Tetrahydrocannabinol (THC) is the primary psychoactive compound in cannabis and what causes the “high.” It is one of more than 100 cannabinoids, or chemical compounds, naturally found in the cannabis plant.

Delta‑9‑THC is the most common and well-studied form, though other forms of THC exist and are less understood.

Federal drug laws place strict limits on delta-9-THC levels. They cap delta-9-THC at 10 milligrams per piece for edibles, and 1,000 milligrams per container for extracts and topicals. Dried cannabis flower and pre-rolled joints have no THC cap, but must disclose the THC level on their labels.

Other intoxicating cannabinoids — like delta-8-THC — are not regulated the same way. Some producers use these other cannabinoids to get around delta-9 limits to make their products more potent.

In 2023, Health Canada issued guidance warning against this practice, noting it could lead to inspections and regulatory action. Its guidance is not legally binding.

“Good weed”

Dr. Oyedeji Ayonrinde, a professor of psychiatry and psychology at Queen’s University, says “good weed” used to mean a product did not contain pesticides or contaminants. Now, it often means a product is high-THC — reinforcing the risky idea that stronger is better.

“We would say, Oh, man, that guy’s got good weed,’ because it’s 30 per cent [THC],” he said.

Today, THC levels average about 25 per cent — up from about four per cent in the 1960s. But some products go as high as 80 or 90 per cent THC.

“That’s ‘the good stuff,’” said Ayonrinde, referring to how consumers view products with these elevated levels of THC.

“One of the major [health] risk factors is the use of cannabis with higher than 10 per cent THC,” said Dr. Daniel Myran, a physician and Canada Research Chair at the University of Ottawa.

Myran led three Canadian studies this year linking heavy cannabis use to health risks such as schizophrenia, dementia and early death.

Chris Blair, a Canadian originally from Jamaica, says the cannabis he once smoked — natural, Jamaican, homegrown weed known as “sess” — was much milder than what is available through Ontario dispensaries today.

“We grew it, it was natural … the regular Mary Jane sess,” he said. “And then times changed … the sess was pushed to almost become the hydro[ponic] type of thing.”

Hydroponic growing methods produce more potent cannabis with higher THC levels. Blair says he could no longer go back to Jamaican sess, because he had built up a tolerance to it.

“Unfortunately, going back to sess was not the same, because it wasn’t the same high or same strength,” he said.

“Back when [I was] smoking [Jamaican sess] … I’d finished that spliff and we were ready to go hang out, we’re ready to party.

“Nowadays, after you smoke you’re mashed and you’re not doing anything.”

Greening out

Ayonrinde says higher THC levels can alter how the brain’s dopamine receptors work, which may induce paranoia.

“Being out of touch with reality, auditory hallucinogens, delusional thoughts, disorganized thinking — that’s part of the mechanism pathway for the development of a severe and enduring mental illness [like] schizophrenia,” he said.

High THC can also worsen anxiety, disrupt sleep, affect mood and trigger psychosis, he says. Other experts cited risks including cannabis use disorder, mental health issues, and dizziness or nausea — sometimes referred to as “greening out.”

Young people, whose brains are still developing until age 25, are most vulnerable to these harmful effects, Ayonrinde says.

During adolescence, the brain undergoes intense growth. “Think of the brain like a construction site,” he said. Frequent, high-dose THC use during this critical period can disrupt dopamine systems and increase the risk of building scaffolding for serious mental health conditions.

While some literature suggests that cannabidiol (CBD) — another major cannabinoid in most cannabis products — may act as a calming, non-psychoactive counterbalance to THC, Ayonrinde says this is only true at extremely high doses, around 6,000 mg.

Standard measurement

Experts say the diversity of cannabis products on the market is part of the challenge.

“When people say, ‘Weed helps me with my trauma,’ an example I often give is: cannabis is just like saying ‘dog’,” said Ayonrinde.

“What breed? Is it a chihuahua or a rottweiler or a great dane? Because without knowing exactly the THC, CBD … what are you talking about?

“There’s no single cannabis.”

Cannabis products lack clear dosage guidelines, and Ayonrinde says marketing messages push consumers to opt for high potency options.

Ruth Ross, a professor of pharmacology and toxicology at the University of Toronto, would like Canada to adopt a standard unit of measurement for THC levels, so consumers could easily understand what one unit means.

“Say a unit was one milligram; they could multiply that up — it’s easy math,” she said.

Myran agrees. “The way we sell alcohol in this country is not set up so that you pay the same amount for a litre of wine as you do for a litre of vodka,” said Myran.

“You have a minimum price per unit of ethanol … and there’s a really compelling reason to price cannabis according to its THC content … [to] financially discourage people from always moving to the highest potency THC products.”

Ross says there is also a need for more current cannabis research. Most cannabis research evaluates the effects of cannabis products with much lower THC levels than those seen on the market today. Long-term health effects can take decades to appear — similar to tobacco.

“Some of [the health harms] might emerge over many, many years, and we don’t know what those will be until data comes in,” she said.

Quebec’s approach

Ross points to Quebec as a unique model in cannabis regulation. It is the only province that caps THC potency and tightly controls how cannabis can be marketed. For example, edibles resembling candy or desserts are prohibited.

Jutras-Aswad, of the Université de Montréal, says overly strict rules can drive some consumers — especially those younger than the province’s legal age of 21 — to the black market.

Still, he says Quebec’s model offers benefits, including greater control over sales and a public health approach focused on harm reduction rather than profit.

Under Quebec’s Cannabis Regulation Act, the Société québécoise du cannabis (SQDC) is the only authorized cannabis retailer in the province.

SQDC employees are trained to offer science-based information, connect consumers with support services and promote safer use.

Researchers in Ontario are now studying how Quebec’s stricter THC limits may be affecting cannabis-related harms compared to other provinces.

“That’s going to be a really interesting within-Canada experiment,” said Ross.

Myran recommends adopting Quebec’s 30 per cent THC caps nationwide.

He also recommends better product labelling requirements and a pricing model that sets a minimum price per unit of THC — to discourage the purchase of high-potency products.

In a 2023 op-ed, Ross argued provinces should fund cannabis research to guide policy and public health.

In it, she notes that Quebec reinvested all $95 million of its 2022 revenue from cannabis sales into prevention and research. By contrast, Ontario set aside just 0.1% of its $170 million in cannabis revenue for a Social Impact Fund that has no clear public health focus.

“Canada can do so much better. We have world experts in cannabis research from coast-to-coast, and we are uniquely positioned to have high-quality, well-funded research on its medical use and potential harms,” she wrote.

“Five years from now, will we be dealing with major public health challenges that could have been avoided?”

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.

From the Montreal Economic Institute

• Canada Post has accumulated $3.8 billion in losses since 2018.
• The Crown corporation is receiving a $1-billion taxpayer loan to stay afloat in 2025-2026.
• Privatization should include an employee share ownership plan.

Privatizing Canada Post and opening up the sector to competition would result in better services and lower prices for Canadians, shows a new publication released by the MEI.

“Canadians are held hostage by a postal system that is inefficient, strike-prone, and, increasingly, financially non-viable,” says Vincent Geloso, senior economist at the MEI and co-author of the report. “We should follow the lead of European countries like Germany that have liberalized and privatized their postal services, with excellent results.”

Canada Post has a federal monopoly on regular letter mail, making it the only entity legally permitted to deliver non-express letters.

The Crown corporation has run deficits for seven straight years, accumulating over $3.6 billion in losses over the past decade.

Meanwhile, letter volume in Canada has fallen from 5.5 billion letters in 2006 to 2 billion in 2024, a 64 per cent decline.

Canada Post’s market share in parcel delivery has also cratered, falling from 62 per cent in 2019 to 24 per cent in 2024, as private competitors have captured more of the growing market.

In December 2024, more than 55,000 Canada Post workers went on a 32-day strike that ground mail and parcel delivery to a halt causing a backlog of nearly 10 million packages, impacting individuals and businesses alike. The strike reportedly cost small businesses an estimated $1.6 billion.

This past May, another union issued a strike notice and began a nationwide overtime ban, again obstructing delivery volumes. Currently, Canada Post employees are voting on the corporation’s latest offer; if the vote fails, there are fears that another strike would ensue.

“There is an inherent problem with monopolies,” explains Mr. Geloso. “No competition means no incentive to be efficient or innovate, which means higher prices by way of increased costs, and consumers are left with no alternative.”

In 1989, Germany decided to open up its market to a limited amount of competition, and by 2008, the sector was fully liberalized.

Privatization of Deutsche Post started in 2000, and currently, the government holds only a small minority stake in the former monopoly.

Today, over 15,000 firms offer some sort of postal service in Germany. The country’s mail service generally outperforms those of other European countries.

In Canada, the cost of sending a letter is 50 per cent higher today than it was in 1989 (inflation-adjusted).

In Germany, postage prices have fallen by 10 per cent over the same period (after accounting for inflation).

The MEI recommends the following steps to kickstart a two-year process of privatizing Canada Post:

• Offer employees shares: This would give workers a stake in the company’s success and help prevent insiders from taking advantage during the transition (i.e., avoid asset-stripping).
• Avoid regulatory capture: A swift reform process would reduce the risk of special interest groups lobbying regulators to lock in unfair advantages in the law.

“Canada Post’s inability to adapt to the changing market shows that it won’t get better on its own; it needs a massive overhaul,” says Mr. Geloso. “Canadians are paying a lot for a second-rate service; Germany showed us how we can turn this around.”

The MEI Economic Note is available here.

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The MEI is an independent public policy think tank with offices in Montreal, Ottawa, and Calgary. Through its publications, media appearances, and advisory services to policymakers, the MEI stimulates public policy debate and reforms based on sound economics and entrepreneurship.