Increasing consumption of energy drinks has raised public health concerns worldwide. The present study intended to contribute to the literature on policies to discourage consumption of these beverages by exploring the effect of front-of-package caffeine warning labels on the purchase intention of young Uruguayan adults. A mixed-methods approach was used to address the research objectives in an online survey with 225 participants aged between 18- and 30-years old. The quantitative component of the survey intended to evaluate the effect of caffeine warnings on purchase intention using choice-based conjoint analysis, whereas the qualitative component explored participants' perceived efficacy of the warnings using an open-ended question. The conjoint task involved a series of choice sets composed of two cans differing in three 2-level variables: octagonal caffeine warning featuring the expression 'Contains caffeine', octagonal sugar warning, and brand. Results from the conjoint analysis showed that caffeine warnings increased choice likelihood, as did the brand conveying energy-related associations. On the contrary, sugar warnings reduced choice likelihood. Responses to the open-ended question provided insights on the lack of efficacy of caffeine warnings and stressed the importance of raising awareness of the potential negative health consequences of energy drink consumption. Taken together results from the present work suggest the importance of designing effective front-of-package warning labels to discourage consumption of energy drinks among young adults.