Here’s what the actual research says about the dangers of cannabis use

A research team parsed 68 current cannabis studies last year on behalf of the Canadian government. The goal was to determine what dangers citizens would face once the drug was legalized. What they learned was science doesn’t know much about cannabis.

Fiona Clement, a health-policy researcher at the University of Calgary’s Cummings School of Medicine, led the group in its study of studies on the subject of human cannabis consumption. Their job wasn’t to determine whether the studies were right, wrong, or conducted properly, it was to get the data from the papers and present it to the government as aggregated findings.

A recent Nature article written by Emily Sohn breaks down the team’s findings as follows:

Of the reviews, 62 showed associations between the drug and various adverse outcomes, including impaired driving, increased risk of stroke and testicular cancer, brain changes that could affect learning and memory, and a particularly consistent link between cannabis use and mental illnesses involving psychosis.

That’s pretty scary stuff, but Canada ended up legalizing cannabis for adult recreational use anyway. And, considering the Canadian government pays for its citizens’ healthcare, that seems bold. Will doing a marijuana cause you to become a forgetful psychotic with testicular cancer? That’d probably be a major burden on the state — especially when you consider that one out of every five adults use cannabis in Canada. So which is it? Scary drug that should be banned, or safe enough for recreational use? Unfortunately, nobody really knows.

Here’s what the team found: cyclic vomiting syndrome and burns top the list of immediate medical dangers — and no, not chemical burns, the researchers are talking about literally burning yourself handling THC in resin form.

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The rate of “cannabis poisoning” in children (meaning, any reported instance of a child ingesting cannabis) has approximately doubled in at least one place where cannabis is legal for adult consumption. One major concern for cannabis users, according to numerous studies, is delayed reaction time impairing their ability to drive.

Habitual use (at least three times a week) has been associated with memory loss and impaired decision-making ability. And then there’s also the hypothesized risk of addiction-like behavior. 

One research team from the University of Texas at Dallas scanned the brains of both cannabis users and people who abstained while they viewed images of cannabis and fruit. The cannabis users’ brains lit up when they saw the weed but weren’t so into the fruit. Predictably, the non-imbibers’ brains preferred the fruit. Potheads like pot more than oranges and bananas, whodathunkit?

The less mirthful findings, like associations to cancer or links to stroke, were tenuous at best and unsubstantiated by further study. The biggest “danger” the Canadian team seems to have found involved concerns that high-potency THC products could have detrimental mental health effects including onset psychosis. The links again seem tenuous, but here’s Nature’s take:

In the largest study yet to assess the connection, scientists analysed data from about 900 people who visited 11 psychiatric-service sites across Europe and Brazil for treatment for their first episode of psychosis. With data from many people over multiple sites — where the availability of high-potency strains varied — the study showed a strong association between daily cannabis use and the likelihood of developing a psychotic disorder. For those who used particularly potent, high-THC strains, the risk was five-fold greater. Assuming a causal connection, the researchers estimated that eliminating the availability of highly potent cannabis would prevent 12% of cases of first-episode psychosis.

There isn’t much to dissect there because these aren’t results, they’re warnings. In essence, a group of scientists took a look at data from several unrelated psychiatric practices and determined that THC was a common factor among many people reporting with onset psychosis. While this is certainly cause for concern, it’s also cause for more research. As the researchers themselves put it:

However, none of the above evidence is causal; only associative evidence is available.

The researchers rated the quality of the studies they looked at between “low” and “moderate.” There simply aren’t any high quality, peer-reviewed, repeatable studies on the long-term effects of natural cannabis on humans. Many of the most popular studies on the subject use synthetic cannabinoids and laboratory mice to obtain their conclusions. 

Unfortunately, in the US, this is unlikely to change until the Federal government lifts prohibition. The US Drug Enforcement Agency lists cannabis as a ‘Schedule I’ drug. According to this classification, it’s among the most dangerous drugs there are. Cocaine, for comparison, is a ‘Schedule II’ drug, despite the fact it killed nearly 14,000 people in the US alone, in just 2017. There are no recorded deaths attributed directly to the consumption of cannabis. 

As long as cannabis is outlawed, only outlaws will conduct reliable large-scale government-funded research trials on recreational cannabis use. Actually, nobody will. And that’s the biggest danger facing adult cannabis consumers today.

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