The association between cannabis and depression: an updated Systematic Review and Meta-analysis

The teenagers in the Kaiser Permanente study were 13 to 17 years old when they reported cannabis use on their health surveys. They were not outliers — adolescent cannabis use has been climbing for fifteen years, accelerated by legalization messaging that described the drug as less harmful than alcohol, sometimes as essentially harmless. In the years that followed their survey, the Kaiser researchers tracked what happened to their mental health. The answers are in the data, published in JAMA in February 2026, and they are not what the cultural conversation about cannabis has been preparing young people to expect.

The teens who had used cannabis in the past year were more likely to be diagnosed with psychotic disorders. More likely to be diagnosed with bipolar disorder. More likely to receive diagnoses of depressive and anxiety disorders. The elevated risks for psychosis and bipolar disorder — the most serious outcomes, the ones that can permanently reshape a young life — persisted into young adulthood, meaning this wasn’t a short-term association that resolved itself. The cohort size makes this hard to dismiss: Kaiser Permanente serves millions of patients, and the division of research that conducted this analysis had both the longitudinal follow-up and the diagnostic records to see what actually happened to the kids who said yes on their health surveys.

This study isn’t isolated. An updated systematic review and meta-analysis published in Psychological Medicine in 2026 found a significant association between cannabis use and later depression. The Lancet Psychiatry published a sweeping review of more than 50 clinical trials and found no high-quality evidence that medicinal cannabis effectively treats anxiety, depression, or PTSD — the very conditions young people frequently report using cannabis to manage. The research gap between the cultural belief (cannabis helps mental health) and the clinical evidence (cannabis may worsen it, particularly in young people) is one of the more striking disconnects in contemporary drug science.

The psychology of why this gap persists is worth naming. In states with legal adult cannabis markets, marketing has normalized use and implied safety. Young people, who already tend toward optimism about personal risk, are receiving messages from peer networks, social media, and even some adults about cannabis’s therapeutic properties — messaging that arrived at the exact moment research on adolescent brain development was becoming clearer about why cannabis and the developing prefrontal cortex are a poor combination. The endocannabinoid system plays a central role in adolescent neurological development. THC disrupts it. The Kaiser study doesn’t tell us the causal mechanism — it can’t, because it’s observational — but the direction of the association is consistent across multiple independent datasets.

For treatment providers, pediatric clinicians, and parents trying to have this conversation, the challenge is that the cultural frame has shifted dramatically and the research hasn’t been loud enough to shift it back. Cannabis legalization is probably the right policy at the adult level — the harms of prohibition are real and well-documented. But legalization happened faster than the public health infrastructure needed to communicate its limits, and adolescents landed in the gap. What follows them out of that gap, the Kaiser study suggests, may be a diagnosis that didn’t have to be.