Cannabis Use by Veterans and Potential Interactions With Antineoplastic Agents: Analysis and Literature Review.

Todorova T.; John E.; Sareen S.; Tandra V.; Davis J.; Lands L.; Weir A. · Federal practitioner : for the health care professionals of the VA, DoD, and PHS · 2026

**Background & Methods** This was a retrospective observational study conducted at the Veterans Affairs Memphis Healthcare System that analyzed electronic health records and survey responses from cancer patients who used cannabis products during antineoplastic treatment. Participants completed surveys during January 2024, and data were compiled to identify potential drug-drug interactions between cannabis and prescribed antineoplastic agents. **Key Findings** • Cannabis use prevalence: 50 of 132 enrolled patients (38%) reported cannabis use within the previous 90 days; 90% were male, and 58% were aged 60-65 years, with 70% predominantly inhaling cannabis products. • Concurrent antineoplastic therapy: Chemotherapy was most common (42% of cannabis users), followed by immunotherapy (38%), targeted therapy (24%), and endocrine therapy (20%). • Potential drug interactions: The analysis identified notable potential interactions between cannabis and antineoplastic agents, with predicted decreased efficacy of immunotherapy and endocrine therapy, and increased toxicity risk with chemotherapy and targeted agents when used concomitantly. **Dosage & Administration** Not reported. The study did not specify cannabis dosages, cannabinoid concentrations (THC/CBD ratios), frequency of use, or specific antineoplastic drug names and doses. **Safety & Adverse Effects** Not reported. The study did not provide detailed documentation of observed adverse effects or toxicity outcomes in patients using cannabis with antineoplastics. Safety data were limited to theoretical interaction predictions based on shared cytochrome P450 metabolism pathways. **Evidence Quality** This is a low-to-moderate quality observational study with significant limitations. The small sample size (n=50 cannabis users) and single-institution design limit generalizability. The retrospective nature and reliance on patient recall of cannabis use introduce recall and selection bias. Most critically, this was a cross-sectional analysis identifying potential interactions rather than measuring actual clinical outcomes; no control group, prospective monitoring, or toxicity/efficacy endpoints were reported. The study level of evidence is approximately 4-5 (observational case series). The authors acknowledge that while cannabis and many antineoplastics share cytochrome P450 metabolism, actual clinical significance remains largely unknown. Future prospective studies with standardized outcome measurements and larger diverse populations are needed.

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