A genetic study estimated that cannabis use raises schizophrenia risk by about a third, supporting a causal link
Using 10 gene variants tied to cannabis use, this Mendelian randomisation study estimated an odds ratio of 1.37 for schizophrenia in users versus non-users, close to the observational estimate of 1.43.
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: Ever-use only, no dose; cannabis variants below genome-wide significance; pleiotropy tests possibly underpowered. Gage 2017 found a smaller cannabis effect and a stronger reverse direction.
The genetic evidence on the other side of the reverse-causation argument.
Significant findings
Vaucher and colleagues took 10 independent gene variants linked to cannabis use in 32,330 people and used them as a stand-in for a randomised trial, then tested schizophrenia in 34,241 cases and 45,604 controls, mostly of European descent.
The genetic estimate: "use of cannabis was associated with increased risk of schizophrenia (odds ratio (OR) of schizophrenia for users vs nonusers of cannabis: 1.37; 95% confidence interval (CI), 1.09-1.67". Their meta-analysis of observational studies gave 1.43 (1.19 to 1.67). The variants "did not show evidence of pleiotropic effects" and adjusting for tobacco did not change the result (OR 1.41; 1.09 to 1.83). They conclude the findings suggest "the relationship is causal".
The other direction
The authors list limits. The study "did not permit investigation of the risk of schizophrenia in relation to the quantity, type, route of administration or indeed the age at exposure to cannabis." The variants "did not reach conventional genome-wide association significance thresholds." They note that tests for pleiotropy "may have been underpowered".
A 2017 Mendelian randomisation study (Gage, Psychological Medicine) found only a small effect of cannabis and stronger evidence that genetic risk for schizophrenia leads to cannabis use. That study is in this library. The two used different genetic data and different ways to express the effect, so their numbers are not directly comparable.
Funding
Swiss National Science Foundation fellowships and the UK Biobank resource. The authors declare no conflict of interest.
What this does not show
It measures ever-use against never-use, not dose, so it cannot confirm or refute the dose-response pattern in observational studies. Nothing here says anyone should start or stop using cannabis or any medication.
Worth asking
How much does the risk depend on how often, how strong, and how young someone starts?
Source
Cannabis use and risk of schizophrenia: a Mendelian randomization study — Vaucher J, Keating BJ, Lasserre AM, Gan W, Lyall DM, Ward J, Smith DJ, Pell JP, Sattar N, Pare G, Holmes MV (2018)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1038/mp.2016.252
DOI: 10.1038/mp.2016.252
How this was scored
- Study design
- Case-control study
- Funding
- Independently funded
- Published in
- Reputable peer-reviewed journal
- Sample size
- 79,845
- Preregistered
- not recorded
- Conflicts disclosed
- Yes
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published October 2, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "moderate evidence". Reasonable evidence with real limitations. It scores 66 out of 100 on our published rubric. One caveat travels with that badge: Ever-use only, no dose; cannabis variants below genome-wide significance; pleiotropy tests possibly underpowered. Gage 2017 found a smaller cannabis effect and a stronger reverse direction. The score is calculated from recorded facts about the source — study design, funding, publication venue, sample size, preregistration — not typed in by an editor.
What is the source for this?
Cannabis use and risk of schizophrenia: a Mendelian randomization study — Vaucher J, Keating BJ, Lasserre AM, Gan W, Lyall DM, Ward J, Smith DJ, Pell JP, Sattar N, Pare G, Holmes MV (2018). Published in: Reputable peer-reviewed journal. DOI: 10.1038/mp.2016.252. The full source is linked on this page so you can read it yourself.
Who paid for this research, and does that matter?
Study design: Case-control study. Funding: Independently funded. Independence from the proponent is not recorded. Industry sponsorship is one of the most reliably measured biases in medicine, which is why funding carries real weight in the score rather than sitting in a footnote.
Is this medical advice?
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.
This is information to bring to your prescriber, not medical advice and not a reason to change anything on your own. Nothing here is an instruction to stop or reduce a medication. If you are in crisis, call or text 988.