An on-premise study to investigate the effects of mixing alcohol with caffeinated beverages

Objective: The purpose of this on-premise study was to determine if mixing alcohol with caffeinated mixers had an impact on objective and subjective intoxication. Methods: The study was conducted across eight drinking occasions in the City of Bristol, UK. Participants (N = 1041) were recruited outside popular night-time entertainment venues and interviewed regarding their alcohol consumption for that particular evening, including whether or not they had consumed caffeinated beverages with alcohol. Subjective intoxication was rated on an 11-point scale and objective intoxication determined with a breath alcohol test. Depending on their consumption on the night of the interview, participants also reported whether they consumed alcohol mixed with caffeinated mixers or alcohol-only on other consumption occasions. Results: Between-subjects analyses found that alcohol–caffeine consumers consumed more alcohol and had higher objective and subjective intoxication than those who consumed alcohol-only. These results remained significant regardless of whether or not they mixed alcohol with caffeinated mixers or consumed alcohol-only on the night of the interview. Within-subject analyses revealed that alcohol–caffeine consumers drank the same or less alcohol on alcohol–caffeine occasions compared to alcohol-only occasions. Conclusions: These findings provide support that alcohol–caffeine use does not increase overall alcohol consumption, and may be one manifestation of a high risk-taking personality.