Why are caffeinated alcoholic beverages especially risky?

Purpose: Evidence suggests that people drink more alcohol and experience more adverse alcohol-related consequences (ARCs) on occasions when they also consume caffeine. The current study examined whether this increase in risk is a result of caffeine attenuating the subjective effects of alcohol intoxication (i.e., the masking hypothesis).
Methods: Undergraduate students (n = 148) reported their drinking patterns using a modified Timeline Followback approach. For each recalled drinking occasion, alcohol consumption, caffeine consumption, perceived blood alcohol concentration, and ARCs were assessed. Generalized linear mixed models were used to examine the influence that alcohol and caffeine consumption had on perceived intoxication and the experience of ARCs.
Results: At the occasion level, greater caffeine consumption was associated with increased consumption of alcohol and increased ARCs. There was also a significant curvilinear relationship between the amount of alcohol consumed and perceived intoxication, such that the more alcohol was consumed on each occasion the less each additional drink increased perceived intoxication. Increased caffeine consumption weakened the association between alcohol consumption and perceived intoxication and it also weakened the association between alcohol consumption and ARCs. Specifically, the weakest relationship between ARCs and alcohol consumption existed at the highest level of caffeine consumption (240+ mg). Caffeine increased subjective intoxication.
Conclusions: These findings do not support the masking hypothesis. Caffeine was strongly associated with ARCs when consumed at high doses and this effect does not appear to be the result of drinking more alcohol or underestimating one's blood alcohol content. Efforts to reduce caffeinated alcohol beverage use are greatly needed.
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