After a first psychotic episode, daily high-potency cannabis tripled the odds of relapse; quitting gave the best course
Among 256 London patients followed two years after first-episode psychosis, daily users of high-potency cannabis "had the worst outcome," odds ratio 3.28 for relapse; former users who stopped "had the most favourable illness course".
Reasonable evidence with real limitations. how we score evidence
Caveat on this rating: Observational; the confidence interval on the main odds ratio runs from 1.22 to 9.18. The companion fixed-effects analysis addresses self-medication and confounding but cannot rule them out entirely. UK cannabis market, 2002 to 2015.
"Can I keep smoking weed on my antipsychotic" is the question, and the answer in this study depends on how much, how strong, and whether you stop.
Significant findings
Schoeler and colleagues (Lancet Psychiatry, 2016) followed patients aged 18 to 65 who presented with a first episode of psychosis in south London between 2002 and 2013, with follow-up to 2015; 256 patients. Relapse meant admission to hospital within two years.
"Simple analyses showed that former regular users of cannabis who stopped after the onset of psychosis had the most favourable illness course with regards to relapse. In multiple analysis, continued high-frequency users (ie, daily use in all 24 months) of high-potency (skunk-like) cannabis had the worst outcome, indexed as an increased risk for a subsequent relapse (odds ratio [OR] 3.28; 95% CI 1.22-9.18), more relapses (incidence rate ratio 1.77; 95% CI 0.96-3.25), fewer months until a relapse occurred (b -0.22; 95% CI -0.40 to -0.04), and more intense psychiatric care (OR 3.16; 95% CI 1.26-8.09) after the onset of psychosis."
A companion analysis by the same group in JAMA Psychiatry the same year, 220 patients with fixed-effects models adjusting for antipsychotic adherence and other drug use, found relapse odds rose during periods of cannabis use relative to periods without (odds ratio 1.13 per period), with cross-lagged analysis pointing from cannabis use to later relapse rather than the reverse.
Worth asking
This is not a drug-drug interaction in the enzyme sense; it is the substance acting on the illness the medication is treating, and the direction held after adjusting for whether people took their antipsychotic. Two things the data support: the dose and potency mattered, and the people who stopped did best. If you have had a psychotic episode and use cannabis, the question for the treating team is not a yes or no but what your pattern is and what the alternative to daily high-potency use would look like.
Source
Effects of continuation, frequency, and type of cannabis use on relapse in the first 2 years after onset of psychosis: an observational study — Schoeler T, Petros N, Di Forti M, Klamerus E, Foglia E, Ajnakina O, Gayer-Anderson C, Colizzi M, et al (2016)
Top-tier peer-reviewed journal
Read the source: https://doi.org/10.1016/S2215-0366(16)30188-2
DOI: 10.1016/S2215-0366(16)30188-2
How this was scored
- Study design
- Cohort study
- Funding
- Independently funded
- Published in
- Top-tier peer-reviewed journal
- Sample size
- 256
- Preregistered
- not recorded
- Conflicts disclosed
- not recorded
- Independent of proponent
- not recorded
- Retracted
- No
Read the full scoring rubric, including what it can't tell you.
Published September 21, 2026.
Questions
How strong is the evidence behind this?
veisund rates this source "moderate evidence". Reasonable evidence with real limitations. It scores 64 out of 100 on our published rubric. One caveat travels with that badge: Observational; the confidence interval on the main odds ratio runs from 1.22 to 9.18. The companion fixed-effects analysis addresses self-medication and confounding but cannot rule them out entirely. UK cannabis market, 2002 to 2015. 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?
Effects of continuation, frequency, and type of cannabis use on relapse in the first 2 years after onset of psychosis: an observational study — Schoeler T, Petros N, Di Forti M, Klamerus E, Foglia E, Ajnakina O, Gayer-Anderson C, Colizzi M, et al (2016). Published in: Top-tier peer-reviewed journal. DOI: 10.1016/S2215-0366(16)30188-2. 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: Cohort 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.