CBD pre-treatment made cannabis worse, not better, for people with schizophrenia
In a double-blind crossover trial, pre-treatment with 1000mg CBD before cannabis inhalation worsened memory impairment and psychotic symptoms in patients with schizophrenia, contradicting the protective hypothesis.
Quick Facts
What This Study Found
CBD pre-treatment resulted in worse delayed verbal recall (3.5 vs 4.8 words, p=0.001) and greater increase in positive psychotic symptoms (5.0 vs 2.9 PANSS-P increase, p=0.01) compared to placebo pre-treatment; CBD did not alter THC or 11-OH-THC plasma levels.
Key Numbers
30 participants; CBD 1000mg vs placebo; delayed recall 3.5 vs 4.8 words (MD -1.3, 95% CI: -2.0 to -0.6); PANSS-P increase 5.0 vs 2.9 (MD 2.2, 95% CI: 0.6 to 3.7); no difference in THC plasma levels.
How They Did This
Double-blind, randomized, placebo-controlled, crossover trial; 30 participants with schizophrenia/schizoaffective disorder plus cannabis use disorder; oral CBD 1000mg or placebo 3 hours before vaporized cannabis (THC 20-60mg).
Why This Research Matters
This directly challenges the popular assumption that CBD protects against THC's harmful effects, particularly in the most vulnerable population.
The Bigger Picture
The idea that CBD in cannabis products might protect against THC-related psychosis has influenced product marketing and harm reduction messaging. This trial suggests the opposite may be true for people with psychotic disorders.
What This Study Doesn't Tell Us
Small sample (n=30); single CBD dose; acute effects only; participants had comorbid cannabis use disorder; may not generalize to healthy volunteers.
Questions This Raises
- ?Why did CBD exacerbate rather than protect against THC effects in this population?
- ?Do patients with schizophrenia metabolize cannabinoids differently?
- ?Should harm reduction messaging about CBD be revised?
Trust & Context
- Key Stat:
- CBD pre-treatment worsened both memory (p=0.001) and psychotic symptoms (p=0.01) after cannabis use in schizophrenia
- Evidence Grade:
- Double-blind crossover RCT provides strong within-subject evidence, though small sample and single acute session limit generalizability.
- Study Age:
- Published 2025
- Original Title:
- Does cannabidiol reduce the adverse effects of cannabis in schizophrenia? A randomised, double-blind, cross-over trial.
- Published In:
- Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(12), 1759-1767 (2025)
- Authors:
- Chesney, Edward(13), Oliver, Dominic(8), Sarma, Ananya, Lamper, Ayşe Doğa, Slimani, Ikram, Lloyd, Millie, Dickens, Alex M, Welds, Michael, Kråkström, Matilda, Gasparini-Andre, Irma, Orešič, Matej, Lawn, Will, Babayeva, Natavan, Freeman, Tom P, Englund, Amir, Strang, John, McGuire, Philip
- Database ID:
- RTHC-06207
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Does CBD protect against THC's effects in schizophrenia?
No. This trial found the opposite. CBD pre-treatment worsened both memory impairment and psychotic symptom increases from cannabis in patients with schizophrenia.
Could this be explained by higher THC levels?
No. CBD did not significantly alter plasma concentrations of THC or its active metabolite, suggesting the mechanism involves drug interaction at the receptor level rather than altered metabolism.
Read More on RethinkTHC
- CBD-oil-quality-guide
- anxiety-medication-after-quitting-weed
- cannabis-chemotherapy-nausea
- cannabis-chronic-pain-research
- cannabis-epilepsy-CBD-Epidiolex
- cbd-anxiety-research-evidence
- cbd-for-weed-withdrawal
- cbd-vs-thc-difference
- medical-benefits-of-cannabis
- quitting-weed-before-surgery
- quitting-weed-medication-interactions
- quitting-weed-pregnancy
- quitting-weed-pregnant
- seniors-older-adults-cannabis-risks-medications
- weed-breastfeeding-THC-breast-milk
Cite This Study
https://rethinkthc.com/research/RTHC-06207APA
Chesney, Edward; Oliver, Dominic; Sarma, Ananya; Lamper, Ayşe Doğa; Slimani, Ikram; Lloyd, Millie; Dickens, Alex M; Welds, Michael; Kråkström, Matilda; Gasparini-Andre, Irma; Orešič, Matej; Lawn, Will; Babayeva, Natavan; Freeman, Tom P; Englund, Amir; Strang, John; McGuire, Philip. (2025). Does cannabidiol reduce the adverse effects of cannabis in schizophrenia? A randomised, double-blind, cross-over trial.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 50(12), 1759-1767. https://doi.org/10.1038/s41386-025-02175-3
MLA
Chesney, Edward, et al. "Does cannabidiol reduce the adverse effects of cannabis in schizophrenia? A randomised, double-blind, cross-over trial.." Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 2025. https://doi.org/10.1038/s41386-025-02175-3
RethinkTHC
RethinkTHC Research Database. "Does cannabidiol reduce the adverse effects of cannabis in s..." RTHC-06207. Retrieved from https://rethinkthc.com/research/chesney-2025-does-cannabidiol-reduce-the
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.