Five U.S. states have proposed requiring health warnings on sugar-sweetened beverages (SSBs). SSB health warnings reduced purchases of these products by 22% in our recent trial, but their mechanisms remain unclear. We sought to identify the psychological mechanisms that explain why SSB health warnings affect purchase behavior.


In 2018, we recruited 400 adult SSB consumers to complete a shopping task in a naturalistic convenience store laboratory in NC, U.S. We randomly assigned participants to a health warning arm (all SSBs in the store displayed a text health warning) or to a control arm (SSBs displayed a control label). Participants selected items to purchase with cash.


Compared to control labels, SSB health warnings elicited more attention, negative emotions (e.g., fear), anticipated social interactions, and thinking about the harms of SSB consumption (range of Cohen’s ds: 0.63-1.34; all p<0.001). Health warnings also increased injunctive norms about limiting SSB consumption (d=0.27, p=0.008) and intentions to limit SSB consumption (d=0.31, p=0.002). In contrast, health warnings did not change other attitudes or beliefs about SSBs or SSB consumption (i.e., added sugar perceptions, healthfulness, appeal/coolness, disease risk perceptions, self-efficacy, response efficacy). Mediators of the effect of health warnings on SSB purchases were negative emotions, anticipated social interactions, thinking about harms, injunctive norms, and intentions to limit SSB consumption (all p<0.05).


SSB health warnings affected purchase behavior by eliciting negative emotions, increasing anticipation of social interactions, keeping the health harms of SSB consumption at top of mind, and shifting norms about beverage consumption. Nutrition warnings may be more effective if they target these mechanisms. Results are consistent with recent studies of why tobacco warnings reduce smoking and point toward a general framework for understanding how health warnings affect behavior.