Background: The purpose of this on-premise study was to determine if alcohol mixed with energy drink (AMED) consumption masks the subjective feelings of intoxication when compared to consuming alcohol only.
Methods: The study was conducted on five nights in the city center of Utrecht. N = 997 people leaving bars were interviewed about their alcohol consumption with and without energy drinks, for that particular evening and for other occasions. People reporting drug and medication use were excluded (N = 84). Subjective intoxication was rated on a 10-point scale. Objective intoxication (breath alcohol concentration, BrAC) was determined with a breath alcohol test. Three groups were identified: (1) the AMED-tonight group (N = 185, 20.2 %), (2) the AMED-other-nights group (N = 246, 27.1 %), and (3) the no-AMED group (N = 482, 52.7 %).
Results: Objective intoxication (BrAC) did not significantly differ (p = 0.94) between the AMED-tonight group (0.074 % ± 0.05), AMED-other-nights group (0.073 % ± 0.05), and the no-AMED group (0.074 % ± 0.05). In line, subjective intoxication was not significantly different (p = 0.96) between the AMED-tonight group (4.5 ± 2.2), AMED-other-nights group (4.6 ± 2.3), and no-AMED group (4.6 ± 2.2). Within-subjects comparisons revealed no significant differences in total alcohol consumption between AMED occasions and alcohol only occasions. Regression analyses showed that "gender" (beta = 0.078, p = 0.016), "time of testing" (beta = 0.085, p = 0.009,) and "BrAC" (beta = 0.574, p = 0.0001) together explained 37.7 % of variance of subjective intoxication scores (Cohen's f (2) = 0.605). Whether or not subjects consumed energy drinks did not predict subjective intoxication scores.
Conclusion: The data suggests that mixing alcohol with energy drink does not mask subjective intoxication.