What Has Canada Learned About Cannabis Since Legalization?

More than 6 years after the legalization of nonmedical cannabis, Canadian scientists are reporting a mix of observations. Legalization has improved drug safety and reduced some health harms yet also raised questions about new high-strength products and consumer decision-making.
Based on the latest 2024 data from Statistics Canda, about a third of adults less than age 45 years have used cannabis during the past year. The rate of regular use seems to be much lower, however. About 10% of those aged < 45 years and 5% of those aged 45 years or more report daily or almost daily use.
Since legalization, 7 in 10 Canadians who used cannabis during the past year said they bought exclusively from the more than 3000 legal cannabis sources nationwide. As a result, cannabis-related drug offences have dropped dramatically. Most of the 10,000 citations in 2022 related to illicit importation or exportation of the drug.
Cannabis-related hospitalizations also declined after legalization, according to a recent study in JAMA Network Open. During the COVID-19 pandemic and subsequent legal market expansion, though, hospitalizations increased again in some provinces, pointing to a potential area for concern.
As cannabis research advances, Canadian scientists are studying various products on the market, health effects during pregnancy and adolescence, and long-term policy considerations.
“Cannabis legalization in Canada led to an initial increase in the number of Canadians using cannabis, which has since levelled off. One benefit of legalization is a greater confidence in product standards and the safety of products, which has the potential to reduce adverse events,” David Hammond, PhD, a professor of public health at the University of Waterloo in Waterloo, Ontario, Canada, told Medscape Medical News. Hammond has evaluated the impacts of cannabis legalization.
“However, legalization has also accelerated the transition to more highly processed and even higher strength products, including high tetrahydrocannabinol (THC) strains of dried flower, THC vapes, and pre-rolled joints infused with concentrates,” he said. “Many consumers have trouble with dosing and overconsume these products, leading to adverse events. There are also concerns about the longer-term health impacts of using high THC products.”
Current Cannabis Research
Nationally, cannabis legalization has mostly focused on setting up the legal market and encouraging consumers to visit legal retail stores, which has “largely been a success,” Hammond said. Revenue from licensed stores has increased steadily, adding about $2 billion to federal and provincial government coffers in 2023.
“In terms of social norms, we’ve not seen any massive shifts, partly because cannabis had relatively high levels of social acceptability before legalization,” Hammond added. “But also, Canada has strong advertising restrictions that have minimized some of the promotional messages that tend to shape social norms, particularly among young people.”
Even so, scientists and policymakers remain curious about cannabis use among young people. In focus groups in recent years, youth and young adults reported easier access, social normalization, and even driving under the influence of cannabis — while operating cars, boats, and recreational vehicles, such as all-terrain vehicles.
“However, the biggest take-home message we heard from youth was that they were not provided the information they needed to make informed decisions,” said Jennifer Donnan, PhD, assistant professor of pharmacy at Memorial University in St. John’s, Newfoundland.
As a result, Donnan and colleagues developed an education program called Drug Education Centered on Youth Decision Empowerment, which is based on harm reduction and prevention strategies linked to the opioid crisis in Canada.
“Many youths are seeing people in their families and communities using cannabis for its medical benefits and for pleasure,” she said. “When they only hear scare tactics to prevent them from consuming cannabis, they start to lose trust.”
Researchers and community members are focused on what happens before birth, too, both among pregnant mothers and within fetal cells. The rate of cannabis use during pregnancy appears to be about 5% in some provinces, and it reaches as high as 20% in some marginalized groups.
“In many cases, women who use cannabis during pregnancy are afraid to say they do, for fear of stigmatization, so it’s important to address these questions about whether there are developmental effects on babies or moms,” said Sandeep Raha, PhD, associate professor of pediatrics at McMaster University in Hamilton, Ontario, and a member of McMaster’s Centre for Medicinal Cannabis Research. 
In preclinical models, Raha and colleagues look at compounds in cannabis — such as THC and cannabidiol — and changes to placental stem cells that are associated with cannabis use. So far, they’ve observed shifts in cellular bioenergetics, which could potentially affect fetal development, the release of certain hormones, and cardiac function. They’ve also observed changes in mammary glands and breast milk.
“The challenging aspect of this research is that we often can’t control for the dosage, concentration, and frequency that happens in the real world,” he said. “But my strong opinion is that cannabis use isn’t safe overall, and we don’t yet understand the full extent of the consequences of legalization.”
Future Research Considerations
As cannabis remains legally accessible, questions remain about the appropriate minimum age for purchase, as well as psychological effects, whether positive or negative, said Steven Laviolette, PhD, professor of psychiatry and director of the Addiction Research Group at the University of Western Ontario in London, Ontario, Canada.
The current cutoff age in Canada is 18 years, but from a developmental and neuroscientific standpoint, the brain continues to change through age 25 years, he said. Future studies may be able to investigate what happens if young adults are exposed to high amounts of cannabis during those years.
In addition, Laviolette and colleagues are studying how THC alters brain signaling pathways and neuroinflammation, which may have implications for certain psychiatric conditions. Changes in the prefrontal cortex or hippocampus, for instance, could link to emotional dysregulation, cognitive concerns, and risk factors for mental disorders such as schizophrenia.
On the other hand, Laviolette’s lab is also investigating interventions and supplements — such as precognitive amino acids — that can reduce neuroinflammation and counteract some of the negative effects of THC. 
“We’re now in the middle of a real-world experiment with millions of people having access,” he said. “Cannabis is a complicated plant with more than 100 phytochemicals, so we’re just beginning to scratch the surface on how all these complicated aspects interact.”
To move forward with beneficial research, though, particularly on controversial topics such as fetal development and psychiatric risks, open communication about the benefits, risks, and ongoing policy considerations is vital, the scientists told Medscape.
“What I would like to suggest to healthcare professionals is that they approach cannabis use with an open mind. For most medical conditions, the evidence is limited and inconclusive, which makes providers uncomfortable,” Donnan said. “However, when patients are presented with resistance or roadblocks to access the care they desire, they may start to lose trust in their healthcare providers and seek advice elsewhere. We need to educate ourselves so we can help patients in a nonjudgmental way to make informed and evidence-based decisions.”
Carolyn Crist is a health and medical journalist who reports on the latest studies for Medscape Medical News, MDedge, and WebMD.
 
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