In 1,922 people treated for mania, continued cannabis went with worse outcomes; those who quit matched never users
Two-year European bipolar cohort: current cannabis users had lower recovery and remission, higher recurrence and greater work impairment than never users; "previous users had similar outcomes to never users".
Suggestive but preliminary. Not settled. how we score evidence
Caveat on this rating: Observational; the "previous user" group is small (4.6 percent) and self-selected. The underlying EMBLEM cohort was a pharmaceutical-sponsored study, which does not bear on the cannabis comparison but is worth knowing.
For bipolar disorder the question is usually asked about lithium or valproate and cannabis. The best data are not about the drug interaction but about what happens to the illness.
Significant findings
Zorrilla and colleagues (Acta Psychiatrica Scandinavica, 2015) used the EMBLEM study, "a 2-year prospective observational study in adults with a manic/mixed episode of bipolar disorder". Groups: current cannabis use (between 12 weeks and 24 months), previous use (during the first 12 weeks only), never use. "Of 1922 patients analyzed, 6.9% were current users, 4.6% previous users, and 88.5% never users."
"Clinical outcomes differed between groups (P<0.019): previous users had highest rates of remission (68.1%) and recovery (38.7%), and lowest rates of recurrence (42.1%) and relapse (29.8%). Logistic regression showed previous users had similar outcomes to never users (all P>0.05), whereas current users had lower recovery (P=0.004) and remission (P=0.014), higher recurrence (P=0.014), greater work impairment (P=0.016), and were more likely not to be living with partner (P=0.006) than never users."
The conclusion: "Bipolar patients who stop using cannabis during manic/mixed episode have similar clinical and functional outcomes to never users, while continued use is associated with higher risk of recurrence and poorer functioning."
Worth asking
Observational, and people who manage to stop cannabis during a manic episode may differ from those who cannot in ways the study could not see. What it shows cleanly is that stopping was not too late: the previous users, who had used in the first twelve weeks and then quit, matched the never users at two years. If you have bipolar disorder and use cannabis, that is the finding to bring to the conversation. The Nayak 2021 row in this wave is the separate, acute danger of psychedelics on lithium.
Source
Cannabis and bipolar disorder: does quitting cannabis use during manic/mixed episode improve clinical/functional outcomes? — Zorrilla I, Aguado J, Haro JM, Barbeito S, López Zurbano S, Ortiz A, López P, Gonzalez-Pinto A (2015)
Reputable peer-reviewed journal
Read the source: https://doi.org/10.1111/acps.12366
DOI: 10.1111/acps.12366
How this was scored
- Study design
- Cohort study
- Funding
- Funding not disclosed
- Published in
- Reputable peer-reviewed journal
- Sample size
- 1,922
- 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 "early signal". Suggestive but preliminary. Not settled. It scores 53 out of 100 on our published rubric. One caveat travels with that badge: Observational; the "previous user" group is small (4.6 percent) and self-selected. The underlying EMBLEM cohort was a pharmaceutical-sponsored study, which does not bear on the cannabis comparison but is worth knowing. 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 and bipolar disorder: does quitting cannabis use during manic/mixed episode improve clinical/functional outcomes? — Zorrilla I, Aguado J, Haro JM, Barbeito S, López Zurbano S, Ortiz A, López P, Gonzalez-Pinto A (2015). Published in: Reputable peer-reviewed journal. DOI: 10.1111/acps.12366. 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: Funding not disclosed. 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.