Influence of package colour, branding and health warnings on appeal and perceived harm of cannabis products among respondents in Canada and the US.

'Plain packaging' and health warnings can reduce appeal and increase risk perceptions of tobacco products. This study tested the effect of health warnings and restricted brand imagery on perceptions of cannabis products. Participants in Canada and the US (n = 45,378) were randomized to view packages of three cannabis brands in 2019. A 3 (health warning) x 4 (brand imagery) between-group factorial experimental design was used. Health warning conditions were: none, Canadian or US warning. The Canadian warning conditions had three messages counterbalanced across brands: pregnancy, adolescent risk, and impaired driving. The US warning mentioned the same broad risk categories. The four branding conditions ranged from packages displaying no brand imagery and uniform colours-'plain packaging'-to full brand imagery. Regression tested differences between conditions on product appeal, perceived harm, and free recall of warning messages. Overall, full branding and plain packaging were rated the most and least appealing, respectively (p < 0.001). Products were rated as significantly less harmful when they had a white background with no or limited branding versus a coloured background (p ≤ 0.01). Products with health warnings were rated significantly less appealing and more harmful than those with no warning (p < 0.001). Message recall was significantly higher for Canadian versus US health warnings, and for the US warning versus no warning (p < 0.001). Message recall was greater among those who saw plain versus fully branded packages for two of the three warning messages (p < 0.01). Prominent health warnings and restrictions on brand imagery may be warranted in jurisdictions considering non-medical cannabis legalization.