Adolescent cannabis use linked to 37% higher depression risk and 3.5x higher suicide attempt risk in young adulthood

The Researcher Behind the Numbers

Why a Meta-Analysis Was Needed

By the late 2010s, the cannabis-psychosis link had been studied extensively. Multiple meta-analyses had established a dose-dependent association between cannabis use and psychotic disorders, particularly with early-onset and high-potency use. But the connection between adolescent cannabis and depression — a far more common condition — remained surprisingly under-synthesized.

Individual longitudinal studies pointed in the same direction, but each had limitations: small samples, short follow-up periods, incomplete adjustment for confounders. Some found significant associations; others didn't. The signal was there, but it was noisy.

The Numbers

The anxiety finding was the surprise absence: OR 1.18 (95% CI: 0.84-1.67, I2 = 42%). Not statistically significant. Given how often cannabis and anxiety are discussed together, the lack of a clear adolescent-onset signal was unexpected.

But the suicidality findings were the ones that stopped people:

The Population Math That Changed Policy

Gobbi's team didn't stop at effect sizes. They calculated the population attributable risk — the proportion of depression cases in young adults that could theoretically be prevented if adolescent cannabis exposure were eliminated.

This number had real-world consequences. In 2019, Gobbi testified before Quebec's parliamentary commission studying Bill No. 2, which proposed raising the province's minimum legal age for cannabis from 18 to 21. Her evidence was part of the case that carried the legislation. Quebec became — and remains — the only Canadian province with a legal cannabis age of 21 instead of 18 or 19.

A subsequent analysis confirmed the policy worked: the increase in cannabis use among 18-to-20-year-olds was 51% lower in Quebec than in other provinces after the age change.

What the Critics Said

The study's reception was overwhelmingly positive — it was published in JAMA Psychiatry, one of the top journals in the field, and has been cited hundreds of times. But legitimate criticisms sharpened the picture.

How This Fits With Other Adolescent Brain Research

Gobbi's meta-analysis is one piece of a converging body of evidence about the adolescent brain's vulnerability to cannabis.

The pattern across these studies is remarkably consistent: the adolescent brain responds differently to cannabis than the adult brain, and the consequences manifest across cognitive, structural, and psychiatric dimensions. Gobbi's contribution was demonstrating that the psychiatric consequences — specifically depression and suicidality — follow the same developmental-vulnerability pattern.

What People Get Wrong

Myth vs. Reality

✕Myth

✓Reality

The Evidence

Evidence-based analysis

The Clinical Implications

For parents trying to navigate conversations about cannabis with their teenagers, Gobbi's findings offer something specific to say: the risk isn't hypothetical, it's quantified. Not as a scare tactic, but as information. A 37% increase in depression risk and a potential 3.5-fold increase in suicide attempt risk are numbers worth knowing, even with the caveats.

For teenagers and young adults who started using early and are now dealing with depression or suicidal thoughts, the study suggests a connection worth exploring with a mental health professional — while also offering the reassurance that the adult brain has more resilience than the adolescent brain.

For policy makers, the population-attributable-risk calculation was the game-changer. Individual risk is modest. Population burden is substantial. That's the math that moved Quebec's legal age from 18 to 21.

Frequently Asked Questions

Does teenage cannabis use cause depression?

This meta-analysis found adolescent cannabis use associated with 37% higher odds of depression in young adulthood, after adjusting for pre-existing mental health. The longitudinal design strengthens the causal argument, but observational studies cannot definitively prove causation. Reverse causation (depressed teens self-medicating) and residual confounding remain possible explanations. The most honest answer: cannabis likely contributes to depression risk in vulnerable adolescents, but it is probably not the sole cause in most cases.

How alarming is the suicide attempt finding?

The 3.46-fold increase in suicide attempt risk is the strongest association found, but it comes with important caveats. Only three studies contributed to this estimate, and the heterogeneity was high (I2 = 61.3%), meaning the true effect size is uncertain. The confidence interval (1.53-7.84) means the actual risk increase could be anywhere from 53% to nearly 8-fold. Even the conservative lower bound is clinically concerning, but the headline number of 3.46x should be cited with appropriate uncertainty.

Does this apply to all forms of cannabis or just smoking?

The included studies primarily captured smoked cannabis from the 1990s and 2000s, at potencies far below today's products. The studies did not distinguish between different cannabinoid profiles, consumption methods, or potency levels. Whether CBD-rich products carry similar risks, or whether high-potency concentrates carry greater risks, remains unknown.

If I used cannabis as a teenager and now have depression, is it because of the cannabis?

It's impossible to know for any individual case. The study identifies a population-level association — among groups of people, those who used cannabis as teenagers had higher rates of depression. But depression has many causes, and many teenage cannabis users never develop it. If you're concerned about a connection in your own life, this is worth discussing with a mental health professional. The encouraging news from other research is that the adult brain shows significant capacity for recovery.

Why didn't the study find a significant link with anxiety?

The anxiety analysis included only three studies, limiting statistical power. The confidence interval (0.84-1.67) was wide enough to include both no effect and a substantial effect. Additionally, the relationship between cannabis and anxiety is known to be bidirectional and dose-dependent — low doses may reduce anxiety while high doses increase it — which could wash out the signal in a meta-analysis that doesn't distinguish dose levels.