Background:
Research is needed on which characteristics of pictorial health warning (PHW) are most likely to reduce tobacco use among Indonesian adolescents. We assessed the effects of different text and image types of PHWs on emotional, motivational and cognitive reactions across key subgroups of Indonesian adolescents.

Methods:
This study used both between- (i.e., text type) and within-subject (i.e., image type) designs, collecting data from adolescents aged 15-18 years (n=280 smokers; n=313 nonsmokers) in Jakarta city and Bogor district. The main independent variables assessed in this study were text type (didactic vs. testimonial) and image type (graphic vs. suffering vs. symbolic). Participants rated each warning for fear, message credibility, message relevance, increasing health concerns, and motivating not to smoke. Adjustment variables include smoking status, sensation seeking, gender, and health topics of the PHWs. To adjust for correlated data due to repeated measures, linear mixed effect models were estimated separately for each outcome, regressing them on warning characteristics and adjustment variables.

Results:
Adolescents rated didactic PHWs higher than testimonials only for message credibility (β=0.31, p=0.015) and increasing health concerns (β=0.25, p=0.048). Symbolic PHWs were rated lower than suffering PHWs on all outcomes (p< 0.001) except for message relevance (β=-0.05, p=0.537), while graphic PHWs were rated higher than suffering PHWs for all outcomes (p< 0.001). Smoking status has no significant effect on fear (β=-0.01, p=0.935), positive effect on message relevance (β=1.45, p< 0.001), but negative effects on message credibility (β=-0.37, p=0.010), increasing health concerns (β=-0.80, p< 0.001), and motivating not to smoke (β=-1.52, p< 0.001). Sensation seeking has significantly negative effects on all outcomes.

Conclusions:
PHWs with graphic imagery and didactic text are likely to have the greatest impact across subgroups of adolescents in low- and middle-income countries like Indonesia. Future studies should explore PHW characteristics that may work better among adolescents with higher sensation seeking.