In a meta-analysis of 4 RCTs, people who used cannabis still improved with trauma-focused therapy for co-occurring PTSD and substance use — but they attended fewer sessions and showed less reduction in non-cannabis drug use.
Read this if you use cannabis and are in or considering PTSD treatment — the therapy can still help, but showing up consistently matters.
What the researchers found
A common clinical concern is that cannabis use might interfere with PTSD treatment — either by numbing emotions needed for therapeutic processing or by signaling lower motivation for change. This meta-analysis of individual patient data from four randomized controlled trials tested that concern directly.
Among 410 patients being treated for co-occurring PTSD and substance use disorders, 33.2% endorsed baseline cannabis use. The results were more nuanced than a simple 'helps or hurts' answer.
Good news first: cannabis users still benefited from treatment. Both trauma-focused and non-trauma-focused therapies produced significant improvements in PTSD symptoms, and trauma-focused treatments produced larger PTSD reductions regardless of cannabis use status. The cannabis didn't block the therapy from working.
But there were costs. Cannabis users attended fewer treatment sessions — a concerning pattern because treatment completion is one of the strongest predictors of long-term outcomes. Cannabis users also showed less improvement in non-cannabis drug use, suggesting that cannabis might be substituting for other substances or reducing motivation to address broader substance use patterns.
The individual patient data approach is what makes this study powerful. Rather than comparing average outcomes across trials, the researchers could examine how cannabis use interacted with treatment type at the individual level, controlling for demographics and other substance use through propensity score weighting.
Why it matters
Clinicians have been uncertain whether to proceed with trauma-focused therapy for PTSD patients who use cannabis. This analysis says: yes, proceed — the therapy still works. But expect lower attendance and be aware that cannabis users may not reduce other substance use as much. This shifts the clinical question from 'should we treat?' to 'how do we maximize engagement and address the full substance use picture?'
The numbers in context
410 patients across 4 RCTs. 33.2% endorsed cannabis use. 70% male. Trauma-focused therapy produced larger PTSD symptom reductions than non-trauma-focused in both cannabis groups. Cannabis users had lower session attendance. Cannabis users showed less improvement in non-cannabis drug use. Propensity score weighting controlled for baseline differences.
How the study worked
Individual patient data meta-analysis from Project Harmony, drawing on 4 RCTs (of 36 total in the larger project) that treated co-occurring PTSD and substance use disorders. Total N=410 (70% male, 33.2% endorsed cannabis use). Propensity score-weighted mixed effects modeling evaluated main and interactive effects of treatment type (trauma-focused vs. non-trauma-focused) and baseline cannabis use on attendance, PTSD symptoms, alcohol use, and non-cannabis drug use severity.
Who was studied
N=4,046 participants from 36 RCTs, with 410 participants reporting cannabis use, 70% male, US-based trials.
What this study cannot tell us
Only 4 of 36 Project Harmony trials included — those that assessed cannabis use at baseline. The 33.2% cannabis use rate may not reflect current patterns (cannabis use has increased since some trials were conducted). Cannabis use was assessed at baseline only — changes during treatment weren't tracked. 'Cannabis use' was binary (yes/no) without dose, frequency, or product information. The 70% male sample limits generalizability to women with PTSD+SUD.
How to read the evidence
Individual patient data meta-analysis of 4 RCTs — a strong study design that allows within-patient analysis across trials. The propensity score weighting strengthens causal inference. Limited by the binary cannabis use measure and baseline-only assessment.
When this study was published
Published in 2024. Project Harmony continues to analyze data across its 36 included RCTs.
The bigger picture
This pairs directly with RTHC-00116 (PTSD predicting substance use over time) and RTHC-00125 (psychological inflexibility linking CUD and PTSD). Together they form a PTSD-cannabis clinical cluster: PTSD drives cannabis use, cannabis use complicates but doesn't prevent PTSD treatment, and psychological inflexibility may be the mechanism linking both. For the cannabis-assisted psychotherapy case report (RTHC-00101), this meta-analysis provides important context — most cannabis use during PTSD treatment is self-directed, not therapeutically structured.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- Would addressing cannabis use directly (rather than just monitoring it) improve PTSD treatment outcomes? Does the lower attendance among cannabis users reflect reduced motivation, symptom self-management reducing perceived need, or practical barriers? Would structured cannabis reduction as part of PTSD treatment improve both outcomes? Is the lesser improvement in non-cannabis drug use a sign of cannabis substitution (replacing other substances with cannabis)?
Read the original research
Cannabis use and trauma-focused treatment for co-occurring posttraumatic stress disorder and substance use disorders: A meta-analysis of individual patient data.
Journal of anxiety disorders, 102, 102827
The Journal of Anxiety Disorders is a reputable peer-reviewed journal that publishes research on anxiety-related conditions.
Citation
Hill, Melanie L; Kline, Alexander C; Saraiya, Tanya C; Gette, Jordan; Ruglass, Lesia M; Norman, Sonya B; Back, Sudie E; Saavedra, Lissette M; Hien, Denise A; Morgan-López, Antonio A. (2024). Cannabis use and trauma-focused treatment for co-occurring posttraumatic stress disorder and substance use disorders: A meta-analysis of individual patient data.. Journal of anxiety disorders, 102, 102827. https://doi.org/10.1016/j.janxdis.2024.102827
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