Cannabis Users with PTSD Still Benefit from Trauma-Focused Therapy — But Attend Fewer Sessions

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.

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?'

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.

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.