Cannabis and hospitalization go hand-in-hand, according to a new study. Cannabis consumers are 22 percent more likely to visit emergency rooms and require hospitalizations. Led by researchers at Unity Health Toronto, they surveyed 4,800 cannabis users over 12 months. They compared the data with 10,000 people who had never used cannabis.
Despite the observational nature of the study, the lead author of the study, Dr. Nicholas Vozoris, told CTV that:
“Our analyses are adjusted and controlled for all of these other factors, making it less likely that the other factors explain the positive emergency department visit and hospitalization finding.”
Observational vs. Experimental Research
Among the reasons for hospitalizations or ER visits, cannabis users reported acute trauma (15%) as the most common cause. Followed by respiratory problems (14%) and gastrointestinal issues (13%).
But the study was observational and therefore unable to say that cannabis use causes higher hospitalization rates. This was a correlational study. Despite the lead researcher’s claim, this study did not test a specific intervention against a control group. All they did was look at the data on particular groups and then form a conclusion.
Observational research can give us insight into what types of connections exist between lifestyle and risks of a specific disease. But all they can do is show correlation. Even the researchers admitted as much, given their small sample size. They said further research is needed to confirm the “possible link between all-cause mortality and respiratory illness.”
Cannabis & Hospitalization Study Bias
Because this was an observational study with no control group, the claim that the study controlled for other factors of hospitalization, like alcohol use, opioid use, prescription drug use, underlying mental health or medical conditions, is patently false.
The study did not compare rates of ER visits and hospitalizations among cannabis consumers to rates among users of alcohol, opioids, prescription drugs, or other substances. The lead researcher, Dr. Vozoris, said he’s unaware of existing research comparing these rates.
Vozoris hopes this study will inform the public that cannabis is not risk-free. But what exactly has this study proven, if anything at all?
The Problem with the Cannabis & Hospitalization Study
Dr. John Ioannidis, a professor at Stanford University, criticizes observational study research. In his paper, “Why Most Published Research Findings are False,” he explains that “research findings may often be simply accurate measures of the prevailing bias.”
And that seems to be the case here.
There’s nothing in this study to indicate why cannabis users would have higher rates of hospitalization and ER visits.
Suppose there are factors the researchers haven’t considered. The only way to truly determine a cause between two variables is to do an experimental study like a randomized control trial. Plenty of observational studies can confirm that cannabis users have higher hospitalization rates. But, without randomized control trials, this correlation tells us nothing.
It’s like the correlation between Nicolas Cage movies and swimming pool drownings. No serious researcher would publish a paper highlighting this correlation, concluding that more observational research was needed, and then remind people that “Nicolas Cage movies aren’t risk-free.”
That’s essentially what has happened here.
That’s why studies like this always call for “further research.” All they have to do is claim a possible connection between cannabis and hospitalization. But with observational research, it is impossible to say x causes y. If anything, “further research” will increase the number of studies claiming a relationship between cannabis and hospitalization, muddying the waters for researchers doing real science.