David Clinton

Back in March 2024, I wrote about some early indications that Canada’s legalization of cannabis was, on balance, causing more harm than good. Well it looks like we’ve now moved past “early indications” and entered the “nervously searching for the exit” stage.

The new concerns follow the recent release of a couple of groundbreaking Canadian studies: Cannabis Use Disorder Emergency Department Visits and Hospitalizations and 5-Year Mortality which found evidence relating cannabis use to early death, and Convergence of Cannabis and Psychosis on the Dopamine System which describes a possible biological mechanism linking cannabis use to psychosis.

Canadian governments had very little moral liability for the medical consequences of cannabis use before they legalized it in 2018. However, legalization predictably led to a near doubling of consumption. In 2012, according to Statistics Canada, just 12.2 percent of Canadians 15 and over had used cannabis in the previous 12 months. By 2022, that number had climbed to 22 percent – representing nearly seven million Canadians. Cases of cannabis use disorder (CUD) treated in Ontario hospitals increased from just 456 in 2006 to 3,263 in 2021.

The government’s decision to legalize the drug¹ has arguably placed millions of additional people at risk of serious health outcomes.

Let’s take a look at the new evidence. The mortality study used hospital care and mortality data for more than eleven million Ontario residents. The researchers were given meaningful access to raw data from multiple government sources and were apparently compliant with all appropriate privacy regulations. They tracked 107,103 individuals who, between 2006 and 2021, were treated in an Ontario hospital for cannabis use disorder.

The main control group used for statistical comparison was all Ontarians. And the secondary control group was made up of individuals with incident hospital-based care for other substance use disorders, like alcohol, opioids, stimulants.

The primary outcome tracked by the study was all-cause mortality. The secondary outcome was mortality subdivided into alcohol poisoning, opioid poisoning, poisoning by other drugs, trauma, intentional self-harm, cancer, infection, diseases of the circulatory system, respiratory system, and gastrointestinal system.

The researchers adjusted for age, sex, neighborhood income quintile, immigrant status, and rurality (urban vs rural residence). They also controlled for comorbid mental health and care for substance use during the previous 3 years.

In other words, this looks like a well-constructed retrospective study based on excellent data resources.

What did they discover? People who received hospital-based care for cannabis use disorder were six times more likely to die early than the general population. And those CUD-related deaths lead to an average 1.8 life-years lost. After adjusting for demographic factors and other conditions, the added risk of early death was still three times greater than the general population. (Although people with CUD incidents were less likely to die young than those with other substance abuse disorders.)

CUD incidents were associated with increased risks for suicide (9.7 times higher), trauma (4.6 times higher), opioid poisoning (5.3 times higher), and cardiovascular and respiratory diseases (2 times higher).

The Convergence of Cannabis and Psychosis study was performed in and around London, Ontario. This one is a bit beyond my technical range, but they claim that:

Elevated dopamine function in a critical SN/VTA subregion may be associated with psychosis risk in people with CUD. Cannabis was associated with the hypothesized final common pathway for the clinical expression of psychotic symptoms.

Which does indicate that there may be more connecting cannabis to overall harm than just social or economic influences.

I’m not suggesting that the government should restore the original ban on cannabis. Like alcohol prohibition, the moment when that might have been possible is now long past. But I am wondering why politicians find it so difficult to wait for even minimal scientific evidence before driving the country over the cliff?