OBJECTIVE To estimate the impact of standardising the colour and branding of disposable vaping devices on young people's interest in trying them.

DESIGN, SETTING AND PARTICIPANTS Data were from national surveys of 16-29-year-olds in Canada, England and the United States in 2023 (N=15 259).

INTERVENTIONS Respondents were randomised (1:1) to view images of either four branded disposable vapes (N=7638) or four standardised white disposable vapes (n=7621) and asked which they would be interested in trying.

MAIN OUTCOME MEASURES The primary outcome was selecting "no interest in trying" rather than any of the vapes displayed. We also examined whether the impact of standardisation differed by five potential moderators.

RESULTS A greater proportion of participants reported "no interest in trying" the white standardised than branded vapes (67.1% vs 62.8%; adjusted risk ratio (ARR) 1.127, 95% CI 1.085 to 1.169). Compared with those who had never smoked or vaped, the impact of standardisation on those reporting no interest was greater for those who had, in the past 30 days, only smoked (47.5% vs 37.5%, ARR 1.287, 95% CI 1.079 to 1.495), only vaped (19.9% vs 16.4%, ARR 1.220, 95% CI 1.002 to 1.438), dual used (13.5% vs 9.5%, ARR 1.420, 95% CI 1.017 to 1.822) or who had formerly vaped/smoked (72.6% vs 65.0%, ARR 1.119, 95% CI 1.071 to 1.167). The impact was also greatest in the oldest age group, but there were no other clear moderators.

CONCLUSIONS Standardising the colour and branding of disposable vaping devices reduces young people's interest in trying them. However, this includes a substantial impact on those who smoke.