Initiation of high-intensity drinking and subsequent substance use in young adulthood.

High-intensity drinking (HID; 10+ drinks/occasion) is associated with acute and long-term risks, including use of other substances. Earlier HID initiation is associated with high-risk alcohol use in young adulthood. Less is known about when HID initiation occurs relative to other substances and how it is associated with subsequent substance use. This study examined survey data from 468 respondents (35.5% female, 65.5% non-Hispanic white) who reported initiating HID by age 20. Weighted descriptive statistics of year of initiation for HID, marijuana, and nicotine were obtained. Weighted linear and logistic regressions examined associations between year and order of HID initiation and age 20 substance use (i.e., nicotine vaping, cigarette use, other tobacco use, marijuana use, marijuana vaping, simultaneous alcohol and marijuana use, and other illicit drug use) and alcohol use disorder (AUD) symptoms. Over half of participants initiated HID after marijuana (54.6%) and nicotine (54.4%). Later HID initiation was associated with fewer AUD symptoms and lower odds of all outcomes except marijuana and other illicit drug use. Initiating HID before marijuana was associated with lower odds of marijuana use outcomes and other illicit drug use at age 20. Initiating HID before nicotine was associated with lower odds of all substance use outcomes at age 20. Earlier HID initiation was associated with risk for subsequent substance use, but initiating HID earlier than other substances was not. Given its association with both alcohol-related outcomes and other substance use in young adulthood, earlier HID initiation is an important target for screening and intervention.