21st birthday drinking and associated physical consequences and behavioral risks.

Twenty-first birthday celebrations often involve dangerously high levels of alcohol consumption, yet little is known about risk factors for excessive drinking on this occasion. Participants (N = 150) from a larger prospective study who consumed at least one drink during their celebration completed questionnaires and semistructured interviews about their 21st birthday within four days after the event. Assessments were designed to characterize 21st birthday alcohol use, adjusted for alcohol content, as well as situational/contextual factors (e.g., celebration location, peer influence) that contribute to event-level drinking. Participants reported an average of 10.85 drinks (9.76 adjusted drinks), with experienced drinkers consuming significantly more than relatively naïve drinkers who had no previous binge or drunken episodes. Men consumed more drinks, whereas age of first drunken episode and heavier drinking during the 3-months preceding the 21st birthday predicted higher estimated blood alcohol concentrations (eBACs) on the 21st birthday. Celebrating in bars and engaging in birthday-specific drinking traditions (free drinks at bars) explained additional variance in 21st birthday eBACs. Both physical consequences (e.g., blacking out or having a hangover) and behavioral risks (e.g., sexually provocative behaviors) were prevalent and were predicted by higher eBACs. Together these findings indicate that 21st birthday celebrations are associated with heavy drinking and a variety of physical consequences and behavioral risks.