Tri-use of alcohol, cannabis, and nicotine in daily life among young adults: A day-level comparison of substance use outcomes to dual-use and alcohol-only use occasions.

Alcohol, cannabis, and nicotine use are common among young adults with many "co-using" substances on the same day. Most co-use research has focused on alcohol and cannabis co-use, but many alcohol + cannabis use days involve nicotine. Nicotine is rarely considered, and such "tri-use" (same-day alcohol + cannabis + nicotine use) may increase one's risk for heavy use and harms. The current daily diary study compared substance use outcomes across tri-use, dual use, and alcohol-only use days. Participants were 99 young adult college students (Mage = 20.28, SD = 1.29) who reported weekly alcohol + cannabis co-use and reported on substance use behavior each day across four consecutive weekends. Multilevel models examined the role of type of use day: tri-use (alcohol + cannabis + nicotine) and dual use (alcohol + nicotine or alcohol + cannabis) compared to alcohol-only use days on the outcomes of number of drinks consumed, odds of heavy episodic drinking (HED; 4-7/5-9 drinks in one day for females/males), odds of high-intensity drinking (HID; 8+/10+ drinks), and odds of experiencing negative substance-related consequences. Participants reported more alcohol and greater odds of HID on tri-use days than alcohol-only days. Participants had higher odds of HID on tri-use days than alcohol + cannabis days. Participants reported more drinks on alcohol + nicotine days than alcohol-only days. Consequences did not differ by type of use day. Findings support that young adults engage in heavier alcohol use on days when nicotine was co-used relative to days with alcohol + cannabis or alcohol-only use. Future studies should continue to consider the role of nicotine use when exploring risks of alcohol and cannabis co-use. (PsycInfo Database Record (c) 2026 APA, all rights reserved).