Effects of mixing alcohol with caffeinated beverages on subjective intoxication: a systematic review and meta-analysis.

It has been suggested that mixing alcohol with energy drinks or other caffeinated beverages may alter the awareness of (or 'mask') intoxication. The proposed reduction in subjective intoxication may have serious consequences by increasing the likelihood of engaging in potentially dangerous activities while intoxicated. A literature search was conducted to collect all studies measuring subjective intoxication after administration of alcohol with energy drinks, or with other caffeinated alcoholic drinks compared with alcohol alone. The studies were critically reviewed and, where possible, included in a meta-analysis in order to determine whether masking exists after mixing alcohol with caffeinated beverages. Sixteen articles were identified, of which nine could be used for the meta-analysis. When including the higher caffeine dose studies, the meta-analysis revealed no significant masking effect (p=0.404). Similarly, when including the lower caffeine dose studies, no significant masking effect was found (p=0.406). Despite the large range of caffeine doses (2.0-5.5 mg/kg resulting in absolute levels of 46-383 mg) and alcohol levels 0.29-1.068 g/kg (resulting in blood alcohol concentration (BAC) from 0.032 to 0.12%) investigated, caffeine had no effect on the judgement of subjective intoxication.