The review, published in the journal Neuroscience & Biobehavioral Reviews, collected research from nine studies on subjective intoxication after consumption of alcohol with energy drinks or with other caffeinated alcoholic drinks compared to alcohol alone.
Researchers from Australia, The Netherlands and the UK said it had been suggested that subjective intoxication, i.e. how drunk someone feels, may be reduced by caffeine consumption, leading to fears of an increased likelihood of engaging in potentially dangerous activities while intoxicated. They said this was based on the hypothesis that the stimulant effects of caffeine ingredients counteract the sedative effects of alcohol.
However, the review found no significant ‘masking’ effects under controlled laboratory conditions, despite the large range of caffeine doses and alcohol levels investigated. They said subjects were generally capable of correctly judging their level of intoxication. Only one of the studies, Heinz et al. (2013), which used a relatively high level of caffeine, found a significant correlation.
Overall, the review suggested that the stimulant effects of caffeine did not modify the subjective experience of intoxicating effects of alcohol across a range of caffeine doses (46–383 mg) and alcohol levels (0.032–0.12% blood alcohol concentration).
Across the studies included, alcohol doses were typically 0.65 g/kg, but ranged from 0.29 to 1.068 g/kg. The resulting blood alcohol concentration ranged from 0.032 to 0.12%. Caffeine doses ranged from 0.6 to 5.5 mg/kg, with the subjective intoxication measured using a variety of means.
When including the higher caffeine dose (4 mg/kg) from Marczinski and Fillmore (2006), the meta-analysis revealed no significant masking effect. Similarly, when including the lower caffeine dose (2 mg/kg) from the same study no significant masking effect was found. Of the individual studies, Heinz et al. (2013) recorded a "significant masking effect". This study used 5.0 and 5.5 mg/kg of caffeine for females and males, respectively, which reduced the effects of alcohol at a blood alcohol concentration of 0.088%, representing a mean absolute dose of caffeine of 220 mg.
The researchers said: “It remains to be seen whether higher levels of caffeine are indeed capable of masking alcohol intoxication in further replications, while noting that Howland et al. (2010) did not report masking after higher levels of both alcohol and caffeine.”
Marczinski and Fillmore (2006) reported an effect at the “margins of significance”.
The researchers said if the masking hypothesis was true this could lead to individuals becoming “uncalibrated” – feeling they were sober, but experiencing the functional impairment associated with alcohol.
“If a masking effect exists, it would not be without consequences. If people underestimate their level of intoxication after consuming AMED [alcohol mixed with energy drink] or alcohol and caffeine compared to alcohol only, they may be more likely to engage in potentially dangerous alcohol-related activities.”
The researchers said driving was a particular concern in this respect.
The paper acknowledged that one of its authors Dr Joris Verster of the Utrecht Institute for Pharmaceutical Sciences had received research support from energy drink brand Red Bull GmbH and acted as a consultant for the Canadian Beverage Association, Centraal Bureau Drogisterijbedrijven, Coleman Frost, Deenox, INSV, Purdue, Red Bull GmbH, Sanofi-Aventis, Sepracor, Takeda, Transcept and the Trimbos Institute.
Likewise Professor Chris Alford of the University of the West of England had in the past received funding from Red Bull GmbH and Sanofi-Aventis and was a scientific adviser to Red Bull GmbH and Sanofi-Aventis, Japan. Meanwhile, Professor Andrew Scholey of Swinburne University in Australia held research grants from Abbott Nutriton, Arla Foods, Baye Healthcare, Cognis, Cyvex, GlaxoSmithKline, Naturex, Nestlé, Martek, Masterfoods, Wrigley, and has acted as a consultant come expert advisor to Abbott Nutrition, Barilla, Bayer Healthcare, Danone, Flordis, GlaxoSmithKline Healthcare, Masterfoods, Martek, Novartis, Unilever, and Wrigley.
The fourth and final author had no potential conflicts of interest to disclose.
Source: Neuroscience & Biobehavioral Reviews
Published online ahead of print, doi: 10.1016/j.neubiorev.2014.07.008
“Effects of mixing alcohol with caffeinated beverages on subjective intoxication: A systematic review and meta-analysis”
Authors: S. Benson, J. C. Verster, C. Alford, A. Scholey