A systematic review of cannabis health warning research

Background: Cannabis legalization provides an opportunity to communicate with consumers through mandated health warnings on cannabis packaging. However, research on cannabis health warnings is a nascent field. Therefore, a review is needed to synthesize cannabis health warning research and inform ongoing policy discussions. Methods: This paper used systematic review guidelines to search online databases, including PubMed Central, Scopus, Web of Science, Jstor, Communication and Mass Media Complete, Medline, PsycINFO, and Google Scholar. Search strings combined the terms "cannabis" or "marijuana" with "health warning" or "health warning message" or "warning label" or "health warning label" or "health information label." Results were synthesized narratively. Results: The search identified 90 research articles. After screening, 17 studies on the impact of cannabis health warnings were retained. Retained studies focused on the hypothetical effects of cannabis health warnings (n = 11; 64.7 %) and "real world" effects of implementing warnings post-legalization (n = 6; 35.3 %). Evidence indicated mandated cannabis health warnings improved noticing and recall of health warning content. Cannabis health warnings describing risks of addiction were consistently rated the least effective. Pictorial cannabis health warnings generally outperformed text-only warnings when displayed on their own, while experiments with warnings on products had mixed results. Cannabis health warnings decreased product appeal, mainly when package branding was minimized. Conclusions: Health warnings on cannabis packaging are an important strategy to communicate risk to consumers. Mandating warnings increased notice, recall, and health knowledge. Warnings with pictures and describing specific risks were most effective, as was showing warnings without product branding.