Reducing cannabis use was linked to less anxiety and better functioning in people with early psychosis
In 110 people with recent-onset psychosis and cannabis problems, reducing cannabis was associated with lower anxiety and improved functioning, but not with changes in psychotic symptoms.
Quick Facts
What This Study Found
This study followed 110 people with early psychosis who also had cannabis abuse or dependence, measuring their substance use and symptoms at four time points over 18 months. Contrary to what many expected, cannabis dose was not associated with positive psychotic symptoms, negative symptoms, relapse, or hospital admissions.
However, greater cannabis use was linked to higher subsequent depression and anxiety. When participants reduced their cannabis use, their anxiety scores dropped and their daily functioning improved. The relationship between cannabis reduction and depression was present but did not reach the threshold for statistical change.
The findings suggest that cannabis in early psychosis may be more relevant to mood and functioning than to psychotic symptoms themselves.
Key Numbers
110 participants studied over 18 months with assessments at 4 time points. Cannabis dose was associated with subsequent higher depression and anxiety. Reductions in cannabis use were significantly associated with reduced anxiety and improved functioning.
How They Did This
Prospective study with repeated measures at baseline, 4.5, 9, and 18 months in 110 participants with early psychosis and comorbid cannabis abuse or dependence. Random intercept models estimated effects of cannabis dose on subsequent clinical outcomes, with substance use measured before psychopathology at each time point.
Why This Research Matters
Early psychosis is a critical window for intervention. If cannabis reduction improves anxiety and functioning without necessarily affecting psychotic symptoms, treatment programs can set more nuanced and achievable goals rather than framing cannabis cessation solely as psychosis prevention.
The Bigger Picture
The relationship between cannabis and psychosis is often presented as straightforward, but this study shows it is more nuanced. In people who already have psychosis, cannabis may primarily affect mood and functioning rather than the core psychotic symptoms, which challenges some common assumptions.
What This Study Doesn't Tell Us
The sample of 110 participants is relatively small. All participants had comorbid cannabis problems, which may not reflect the broader early psychosis population. Self-reported cannabis use may not be fully accurate. The study cannot establish causation.
Questions This Raises
- ?If cannabis primarily affects mood and functioning rather than psychotic symptoms in early psychosis, should treatment messaging be reframed?
- ?Would the results differ with a larger sample or longer follow-up?
- ?Does the type or potency of cannabis matter?
Trust & Context
- Key Stat:
- Cannabis reduction linked to lower anxiety and improved functioning
- Evidence Grade:
- Prospective longitudinal study with repeated measures, but relatively small sample size.
- Study Age:
- Published in 2015 with 18 months of follow-up data.
- Original Title:
- The impact of cannabis use on clinical outcomes in recent onset psychosis.
- Published In:
- Schizophrenia bulletin, 41(2), 382-90 (2015)
- Database ID:
- RTHC-00911
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Does cannabis make psychosis worse?
In this study, cannabis use was not associated with worsening psychotic symptoms, relapse, or hospitalization. It was linked to higher anxiety and depression, and reducing use improved anxiety and daily functioning.
Should people with psychosis stop using cannabis?
This study found that reducing cannabis use was associated with less anxiety and better daily functioning, suggesting potential benefits to cutting back, even if psychotic symptoms were not directly affected.
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Cite This Study
https://rethinkthc.com/research/RTHC-00911APA
Barrowclough, Christine; Gregg, Lynsey; Lobban, Fiona; Bucci, Sandra; Emsley, Richard. (2015). The impact of cannabis use on clinical outcomes in recent onset psychosis.. Schizophrenia bulletin, 41(2), 382-90. https://doi.org/10.1093/schbul/sbu095
MLA
Barrowclough, Christine, et al. "The impact of cannabis use on clinical outcomes in recent onset psychosis.." Schizophrenia bulletin, 2015. https://doi.org/10.1093/schbul/sbu095
RethinkTHC
RethinkTHC Research Database. "The impact of cannabis use on clinical outcomes in recent on..." RTHC-00911. Retrieved from https://rethinkthc.com/research/barrowclough-2015-the-impact-of-cannabis
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.