Two adolescent drinking milestones were used as primary outcomes among adolescent ever-drinkers: age of first intoxication, a common and clinically relevant variable, and first DSM-5 alcohol use disorder symptom, a heritable characteristic associated with future alcohol-related problems (Rhee et al., 2003; Young et al., 2006). These outcomes commonly occur during adolescence and therefore coincide with the environment of adolescent peer drinking. Age of first intoxication was derived from responses to the question “How old were you the first time you got drunk, that is, your speech was slurred or you were unsteady on your feet?” Age of first DSM-5 symptom was developed from examining the youngest age that individuals first experienced one of the 11 symptoms of alcohol use disorder. Given the longitudinal design of this study with multiple assessments over time, the earliest interview in which the participant endorsed first intoxication or first DSM-5 symptom was selected to assign the age of onset.
