Methods: As part of a prospective randomized community trial, Evaluating Community-Driven Strategies to Prevent Underage Drinking Parties, we conducted a repeated cross-sectional online survey of 15 to 20-year-olds. An address-based sampling approach was used to recruit 15-20-year-olds residing in 24 communities in seven states to participate in the survey. The survey assessed experiences at the last party attended with alcohol, including party characteristics (size, gender and age composition, location) and self-reported substance use and consequences. Data collected in 2015 and 2016 from 1512 (55.2% female, 75.9% White, mean age: 18 years old) youth and young adults who reported ever attending a party with alcohol were used for analyses. Bivariate linear regression models were used to examine associations between simultaneous use of alcohol and marijuana and the number of consequences (unprotected sex, car crash, physical fight, punished by parents, and having a hangover) experienced at the last party they attended.
Results: Among youth and young adults who attended a party with alcohol, 152 (10.1%) used alcohol and marijuana simultaneously, 575 (38.0%) used alcohol-only, 33 (2.2%) used marijuana-only, and 752 (49.7%) did not report substance use at the last party attended. Those who reported simultaneous use of alcohol and marijuana were significantly more likely to experience a greater number of acute consequences compared to those who used only alcohol (β:0.47, SE:0.12; p<0.001) or only marijuana (β:0.33, SE:0.06; p<0.001). There was not a statistically significant difference in the number of consequences experienced by those who used only alcohol or marijuana at the last party. Youth and young adults attending large parties (β:0.07; SE:0.03; p=0.007) were significantly more likely to report experiencing a greater number of acute consequences, and fewer consequences at parties with majority of attendees over 21 (β:-13; SE:0.05; p=0.004).
Conclusions: Our findings suggest that simultaneous use of alcohol and marijuana in a party context increases the risk of experiencing acute consequences among youth and young adults. Prevention strategies should consider the simultaneous use of alcohol and marijuana at parties to reduce harms among youth and young adults.