Across 22 Longitudinal Studies, Cannabis Use Tracked With Higher Odds of Later Depression | Research

The takeaway

Pooling 22 cohorts, cannabis use was associated with about 29 percent higher odds of later depression, with medium overall bias risk and weak exposure measurement across studies.

Readers tracking mental health outcomes in cannabis policy, adolescent health researchers, and anyone comparing cross-sectional claims with longitudinal evidence.

OR 1.29
pooled odds of later depression among cannabis users versus non‑users across 22 longitudinal studies

What the researchers found

When researchers combined results from 22 longitudinal studies that adjusted for baseline depression, cannabis users had higher odds of later depression than non‑users. The pooled odds ratio was 1.29, which translates to roughly 29 percent higher odds on average. Most included samples were adolescents and many were based in the United States. Risk of bias was rated medium overall, with the biggest concern being how cannabis exposure was measured. Funnel plot and Egger testing did not flag publication bias. The signal is consistent across cohorts but modest in size and based on observational data.

Why it matters

Debates about cannabis and mental health often cite cross-sectional snapshots that cannot separate cause from correlation. This project aggregated only longitudinal studies that accounted for baseline depression, offering a clearer look at whether cannabis use is followed by higher odds of later depression in real-world cohorts during a period of shifting laws and rising potency.

The numbers in context

- Pooled association: OR 1.29 (95% CI 1.13 to 1.46). About 29 percent higher odds of later depression among cannabis users

- Studies pooled: 22 longitudinal cohorts, most with participants under 18 at baseline

- Geography: 11 studies conducted in the United States

- Bias rating: medium overall, driven largely by weak exposure measurement

How the study worked

Systematic review and meta-analysis of longitudinal human studies that measured cannabis use, controlled for depression at baseline, and assessed later depression outcomes. The team screened 1,599 titles across databases and included 22 studies in the meta-analysis. Random effects models were used, along with multilevel meta-regression to explore moderators. Eleven studies were from the United States and most participants were under 18 at enrollment. Risk of bias was assessed and rated medium overall, with exposure measurement as a key weakness. Publication bias was evaluated using a funnel plot and Egger's Sandwich test, which did not suggest bias.

Who was studied

22 longitudinal studies, mostly US-based, participants mostly under 18

What this study cannot tell us

Observational evidence only. Even with baseline adjustment, unmeasured confounding can explain part of the signal. Cannabis exposure was inconsistently measured, often as any use versus none, with little information on frequency, potency, product type, route, or duration. Most participants were adolescents, which narrows generalizability to older adults. Heterogeneity in how depression was assessed across cohorts can affect comparability. Funding sources and conflicts were not reported in the abstract. There is a timeline inconsistency in the provided materials, which cite a 2014 publication but describe a search window extending to March 2023; if this reflects an updated analysis that retained the original author list and title, the pooled estimate may differ from the 2014-only dataset.

How to read the evidence

Rated strong for consistency across 22 longitudinal cohorts with baseline depression adjustment and no publication bias signal. The grade is tempered by observational design, medium risk of bias, and weak exposure measurement.

When this study was published

Cited as 2014 in Psychological Medicine, but the abstract describes a search through March 2023 that included and extended the original dataset. If this reflects an updated analysis, results may differ from the 2014-only meta-analysis. Either way, many included cohorts predate today’s higher-potency, diversified product landscape.

The bigger picture

A modest association that repeats across many cohorts can still matter at the population level. Here, the effect size is small to moderate and the studies are observational, so residual confounding remains on the table. Exposure was often captured as a simple yes or no rather than frequency, potency, or product type. That limits what can be said about dose, trajectory, or risk in the current market where concentrates and high-THC products are common. The design choice to adjust for baseline depression supports a temporal link, but it does not establish causation or rule out shared risk factors such as family history, early adversity, or co-use of alcohol and nicotine.

Replication

Not stated in abstract.

Funding

Not reported in abstract.

Conflicts of interest

Not reported in abstract.

Questions still open

Does the association vary by age of initiation, frequency, potency, or product type?
How do co-occurring factors like alcohol, nicotine, or early life stress shape the cannabis–depression link?
Do symptoms change after reducing or stopping cannabis use, and how long does that take?
Are certain subgroups, such as those with family risk for mood disorders, more strongly affected?

Common questions

Does this prove cannabis causes depression?

No. These are longitudinal observational studies that adjusted for baseline depression. They show cannabis use was followed by higher odds of later depression, but shared risk factors or residual confounding could explain part of the link.

How big is the association?

The pooled odds ratio was 1.29. In plain terms, cannabis users in these cohorts had about 29 percent higher odds of later depression on average compared with non‑users.

Who was studied?

Mostly adolescents from 22 longitudinal cohorts, about half of which were in the United States. Measures of cannabis exposure were often simple yes or no rather than detailed frequency or potency.

Read the original research

The association between cannabis use and depression: a systematic review and meta-analysis of longitudinal studies

Psychological Medicine, 44(4), 797-810

Psychological Medicine is a well-regarded journal in the field of psychiatry and psychology.

View on PubMed ↗Publisher’s paper ↗

Citation

Lev-Ran, Shaul; Roerecke, Michael; Le Foll, Bernard; George, Tony P.; McKenzie, Kwame; Rehm, Jurgen. (2014). The association between cannabis use and depression: a systematic review and meta-analysis of longitudinal studies. Psychological Medicine, 44(4), 797-810. https://doi.org/10.1017/S0033291724003143