Cannabis And Schizophrenia

The increasingly important question about the potential harms of marijuana


Pictured: Smells delicious. Oddly enough, I love the smell of weed, but it gives me the worst migraines. Photo by Ryan Lange on Unsplash

Marijuana is one of the perennial topics that I've been writing about almost since I started putting these articles together. It’s one of those wonderful things that we like to think of as somewhat bad for our health, but also secretly wish could cure our healthcare issues. Every six months, you see a story positioning weed as either something that will destroy our lives, or save us all, which is great fun because it’s just a plant, not the herald of Ragnarök.

Stock photos for Ragnarok are now all Marvel-based depictions of Thor, which is both apt and somewhat disappointing. Where are the Frigg fans? Photo by ANIRUDH on Unsplash

Recently, this fear has raised its head yet again. A swathe of headlines have cropped up saying that cannabis is causing 30% of schizophrenia in young men, which sounds terrifying on its face.

Fortunately, the evidence isn’t quite that strong. While cannabis isn’t a perfect cure for all of your ills, it also isn’t destroying the very fabric of society itself.

Let’s look at the data.

The Data

The new study that has the headlines screaming about marijuana is a national cohort paper looking at people aged 16–49 in the entire country of Denmark between 1970 and now. If you think that’s very impressive, well, yes I’d agree it’s absolutely amazing and as an epidemiologist I’m EXTREMELY jealous.

Sometimes I dream of moving to a Nordic country. Then I go for a snorkel in the Sydney sun and remember why I love Australia. Photo by Nick Karvounis on Unsplash

The researchers looked at every new diagnosis of schizophrenia in the country in the last 50 years, as well as all of the diagnoses of substance use disorders. They found that, after correcting for age and a few other potential confounders like parental history of mental health and country of birth, there was a substantially increased risk of schizophrenia in people who also had a diagnosis of cannabis use disorder.

The researchers then calculated what’s called a Population Attributable Risk Fraction for cannabis use disorders and schizophrenia. What this number means is the portion of schizophrenia…