Intrapersonal and interpersonal pathways linking 21st birthday celebration beliefs, intentions, and drinking behavior.

In the United States, turning 21 often involves heavy drinking and high rates of alcohol-related consequences. Friends are an important source of social influence on young adult drinking, including during 21st birthdays. However, research is needed to investigate the specific pathways through which this interpersonal influence occurs. Data were drawn from a larger intervention study focused on reducing 21st birthday drinking. Using data from 166 celebrant and friend dyads (N = 332 individuals), we prospectively examined relations among each person's beliefs about 21st birthday celebrations, drinking intentions for the celebrant, and celebrants' estimated blood alcohol concentration (eBAC) on their 21st birthdays. Path analyses evaluated the impact of celebrant and friend beliefs on their own report of celebrant intentions, each other's report of celebrant intentions, and celebrant eBAC, as well as the mediating role of each individual's report of celebrant intentions. Results revealed significant indirect effects of each individual's beliefs on celebrant eBAC via their own report of celebrant 21st birthday drinking intentions. Friend beliefs also predicted celebrant eBAC via celebrant drinking intentions, beyond the effect of celebrant beliefs. Importantly, celebrant eBAC was as strongly predicted by friend 21st birthday celebration beliefs as they were by their own beliefs. Results highlight multiple pathways through which friends influence 21st birthday drinking and reveal that friend influence is not constrained to the celebration, but begins in advance of the event by shaping celebrants' drinking intentions. Findings highlight key directions for future work leveraging friends as intervention agents to reduce drinking related to this high-risk event.