The acute effects of caffeinated versus non-caffeinated alcoholic beverage on driving performance and attention/reaction time


Jonathan Howland, Department of Community Health Sciences, Boston University School of Public Health, 801 Massachusetts Avenue, Crosstown Center—3rd Floor, Boston, MA 02118, USA. E-mail:


Aims  Marketing that promotes mixing caffeinated ‘energy’ drinks with alcoholic beverages (e.g. Red Bull with vodka) targets young drinkers and conveys the expectation that caffeine will offset the sedating effects of alcohol and enhance alertness. Such beliefs could result in unwarranted risk taking (e.g. driving while intoxicated). The aim of this study was to assess the acute effects of caffeinated versus non-caffeinated alcoholic beverages on a simulated driving task and attention/reaction time.

Design  We conducted a 2 × 2 between-groups randomized trial in which participants were randomized to one of four conditions: beer and non-alcoholic beer, with and without caffeine added. Caffeine was added in the same proportion as found in a commercially available caffeinated beer (69 mg/12 oz of beer at 4.8% alc. by vol).

Participants  Participants were 127 non-dependent, heavy episodic, young adult drinkers (age 21–30) who were college students or recent graduates. The target breath alcohol level was 0.12 g%.

Measures  Driving performance was assessed with a driving simulator; sustained attention/reaction with the Psychomotor Vigilance Task (PVT).

Findings  Across the driving and attention/reaction time we found main effects for alcohol, with alcohol significantly impairing driving and sustained attention/reaction time, with mainly large statistical effects; however, the addition of caffeine had no main or interaction effects on performance.

Conclusion  The addition of caffeine to alcohol does not appear to enhance driving or sustained attention/reaction time performance relative to alcohol alone.