Effects of textual warnings and warning symbols on cannabis advertisements on product perceptions among US young adults.

States with legalized non-medical cannabis require different warnings on packages and advertisements; yet, studies examining effects of textual warnings and different warning symbols on young adults' perceptions are limited. In 2024, US young adults ages 18-34 (n = 3 579) completed an online survey-based experiment using a 2 × 4 factorial design (textual warning: no, yes; warning symbol: none, leaf, THC, leaf + THC), then reported on 5 perception outcomes: addictiveness, harm, cautiousness, appeal, and interest. Multivariable regressions assessed these conditions and their interactions in relation to outcomes, overall and by past-month cannabis use status. Among participants without past-month use, the THC symbol (versus none) was associated with higher perceived addictiveness (B = 0.32, SE = 0.12), harm (B = 0.23, SE = 0.12), and cautiousness (B = 0.31, SE = 0.13); the textual warning was associated with greater appeal (B = 0.18, SE = 0.09). No effects were found among participants reporting cannabis use. An interaction between textual warning × leaf symbol on perceived harm (B = 0.35, SE = 0.18) indicated that exposure to both the textual warning and leaf symbol decreased perceived harm; exposure to only one (i.e. not together) increased perceived harm. Regulatory bodies must understand effects of different warning requirements, consider requiring the THC symbol, assess potential confusion of the leaf symbol, and explore warnings targeting different subgroups.