IMPORTANCE e-Cigarette vaping among youths and adults has increased in Great Britain. The design of e-cigarette packaging may appeal to youths. Regulations that reduce the appeal of e-cigarettes to youths may deter adult smokers from trying e-cigarettes to help them quit smoking.

OBJECTIVE To examine the association of fully branded and standardized e-cigarette packaging with interest in trying products among youths and adults in Great Britain.

DESIGN, SETTING, AND PARTICIPANTS In this survey study comprising 2 surveys, the online Action on Smoking and Health Smokefree Great Britain survey collected data between March 25 and April 16, 2021, from a representative sample of 2469 youths (aged 11-18 years) and between February 18 and March 18, 2021, from a representative sample of 12 046 adults (aged ≥18 years).

INTERVENTIONS A between-individuals experimental design was used to examine participants' perceptions of e-cigarette packs that were digitally altered to remove brand imagery and color. Participants were randomly assigned to view a set of 3 e-cigarette packs from 1 of 3 different packaging conditions: (1) fully branded packs (control), (2) white standardized packs with brand name, or (3) green standardized packs with brand name.

MAIN OUTCOMES AND MEASURES Youth participants were asked which product people their age would be most interested in trying, while adult participants were asked which product they would be most interested in trying. All participants could respond "no interest" or "don't know." Logistic regression models tested whether reporting no interest in trying the e-cigarettes differed between the pack conditions.

RESULTS This study included 2469 youths (1286 female youths [52.1%]; mean [SD] age, 15.0 [2.3] years) and 12 046 adults (6412 female [53.2%]; mean [SD] age, 49.9 [17.4] years). Youths had higher odds of reporting no interest among people their age in trying the e-cigarettes packaged in green (292 of 815 [35.8%]; adjusted odds ratio [AOR], 1.37; 95% CI, 1.10-1.71; P = .005) but not white (264 of 826 [32.0%]; AOR, 1.16; 95% CI, 0.93-1.44; P = .20) standardized packaging compared with the fully branded packaging (238 of 828 [28.7%]). Adults had lower odds of reporting no interest in trying e-cigarettes in green standardized packaging (3505 of 4040 [86.8%]; AOR, 0.85; 95% CI, 0.73-0.99; P = .046) but not white packaging (3532 of 4006 [88.2%]; AOR, 1.05; 95% CI, 0.89-1.23; P = .59) compared with branded packaging (3526 of 4000 [88.1%]). Youths who had never vaped (275 of 699 [39.3%]; AOR, 1.34; 95% CI, 1.07-1.69; P = .01) and youths who had never smoked (271 of 676 [40.1%]; AOR, 1.38; 95% CI, 1.10-1.75; P = .006) were more likely to report no interest in trying e-cigarettes in green packaging compared with branded packaging (224 of 688 [32.6%] never vaping; 216 of 662 [32.6%] never smoking). There were no significant differences by vaping or smoking status among adults.

CONCLUSIONS AND RELEVANCE The findings of this survey study suggest that standardized packaging measures may reduce the appeal of e-cigarettes among youths without reducing their appeal among adults.