Discussion
We evaluated the potential impact of health warning labels on thinking about health risks, attitudes, and intention to change alcohol consumption among young adults in Mexico. We found that participants exposed to a can of beer with a health warning label were more thoughtful about the health risks of drinking beer than the control group. Also, a lower percentage of young adults in intervened vs control group considered the product attractive, especially among those observing the health warning label in yellow. Although not statistically significant, more participants in the health warning label in yellow mentioned they avoided seeing the label. Neither was statistically significant, but a lower percentage of participants in the intervention groups, especially those who observed a yellow health warning label, considered buying or consuming the product than the control group. Our post-hoc analyses showed that participants assigned to health risks and mental health messages thought more frequently about the health risks involved in drinking than those who observed messages about prohibitions on sale and consumption.Our findings related to thinking about health risks are consistent with prior studies that found higher frequency of thinking about alcohol health risks alcohol in the groups exposed to health warning labels compared to controls [Fewer participants in the intervention groups found the can of beer attractive, suggesting that exposure to warning labels can lead to developing negative attitudes toward the product [Although we did not find statistically significant differences in the intention to consume or purchase across experimental groups, we did observe a lower percentage of participants in the intervention groups with the intention to consume or purchase the beer can presented. The results of the potential effect of warning labels on intent to purchase and consume alcoholic beverages have been inconsistent across studies. Clarke, et al., experimented in a naturalistic shopping lab (a space with similar characteristics to a supermarket) and found that the selection of alcoholic beverages was not different between study groups [That studies find no difference or differences of great magnitude in the intention to change in purchases and consumption of alcohol may be an expected result in studies where participants are exposed only once to warning messages. The study by Zhao et al., the largest real-world experiment conducted until now, found a reduction in per capita alcohol sales after 14-month exposure to health warning labels with rotating health and safety messages as compared to control sites [As an exploratory analysis, we also evaluated the potential effect of groups of messages on participant's responses. The results showed that health warning messages associated with mental health problems seemed to have a greater impact on thinking about health risks and avoiding seeing the label than those related to banning the sale or consumption of alcohol. Currently in Mexico, only the pictogram related to prohibiting the sale of alcohol to minors is mandatory in beer cans [Our study has limitations including not reaching the expected sample size, which could explain why we did not detect some differences in outcomes between study groups. Although the study sample was balanced for most of the variables collected, random differences might remain given that we used simple randomization and the sample size was insufficiently large. Also, the representativeness is limited to students with upper-middle and upper-level education and access to internet. We could also assume that the study sample better represents students of upper-middle education in whom a field of specialization is not expected and in whom the educational and employment status was not asked by an error in the online questionnaire. Further studies are required to determine the consistency of findings in populations with more diverse characteristics (e.g., in populations with lower educational levels) and in environments closer to reality (e.g., purchasing laboratories). Likewise, it will be necessary to replicate the study in a larger study sample to evaluate: 1) which type of labeling (red or yellow) is more suitable for the population in Mexico, 2) the use of symbols versus authentic images (such as those presented on cigarette packs), 3) the understanding of warning messages and 4) the deterrence capacity of different warning messages. Finally, we cannot rule out the possibility that the impact of health warning labels is different in other alcoholic beverages. We focused on studying the potential impact of health warning labels on beer cans among consumers of this type of beverage not only because it is the alcoholic beverage most consumed in Mexico but also to avoid that preferences could influence the estimations.