The landscape of cannabis use in the US is continually evolving as more states decriminalize or legalize recreational cannabis use. Young adults have been found to report greater prevalence of cannabis use than older adults (Patrick et al., 2024) as well as higher problematic cannabis use (Haug et al., 2017). Among young adult college students, 39.5% report past-year cannabis use and 6.3% report daily use (Patrick et al., 2024). Importantly, young adults are more likely to use cannabis if they do not view cannabis as risky (Burrow-Sánchez & Cohen, 2025), despite many experiencing cannabis-related harms, including driving under the influence (Caldeira et al., 2008, Pearson et al., 2017) and cannabis use disorders (CUD; Caldeira et al., 2008, Gunn et al., 2020). Young adult college students who co-use alcohol and cannabis – particularly individuals who simultaneously use alcohol and cannabis (i.e., use of alcohol and cannabis at the same time so that effects overlap) – represent a particularly higher-risk group of college students as co-use is linked with increased risk for substance related harms overall and in daily life (see Lee et al., 2022, Linden-Carmichael et al., 2020). In addition, co-use is on the rise among college students (Hai et al., 2022) and individuals aged 21 years and older (Gonçalves et al., 2023). Recent work supports that fewer young adults and college students exclusively use cannabis than young adults or college students who co-use alcohol and cannabis (Linden-Carmichael et al., 2021, Looby et al., 2021).

In tandem with increases in prevalence of cannabis use, numerous types (e.g., plants, concentrates) and modes (e.g., joints, vaping) of cannabis are available for consumers and are differentially linked with risk for cannabis use outcomes. Cannabis flower is generally the most prevalent type of cannabis used (Inman & Cservenka, 2024), with 70.4% of college students who use cannabis predominately using cannabis flower on cannabis use occasions (McCool et al., 2025). Cannabis flower THC potency and use of cannabis concentrates are both linked to increased risk for CUD (Inman and Cservenka, 2024, Piercey et al., 2024). Regarding modes, joints are generally the most prevalent mode among college students and bong use is associated with more negative consequences than other modes (McCool et al., 2025, Swan et al., 2021). Some college students report preference for bong and joint use than other modes of use for achieving a “better high” and for convenience (Thompson et al., 2024). Perceived risk varies across mode of cannabis use, with dabbing and vaping perceived as higher-risk modes of use (Florimbio et al., 2023).

Although recent research supports variations in cannabis use outcomes by type and mode of use, it is important to note most extant research on types and modes of cannabis has relied on between-person, cross-sectional studies (e.g., Florimbio et al., 2023, Gunn et al., 2020, McCool et al., 2025, Meier, 2017, Swan et al., 2021, Thompson et al., 2024). Within-person, daily diary studies are ideal for identifying how select use behaviors (e.g., type, mode of use) are differentially associated with cannabis use outcomes (e.g., level of use, harms). Within-person studies exploring variability in mode of cannabis are particularly ideal given recent work supporting that use of multiple modes within the same week is prevalent (Streck et al., 2019). Diary studies allow for comparisons of how cannabis use types and modes on a given day correspond to use outcomes within the same individual. Such information is critical for informing targeted, real-time intervention. To date, several studies have examined differences in cannabis use types and modes on outcomes in daily life (e.g., Cloutier et al., 2022, Hughes et al., 2014, Stevens et al., 2021, Streck et al., 2019). Daily diary studies have found that bong use was the most common mode of cannabis use (Cloutier et al., 2022, Hughes et al., 2014), with participants feeling the most intoxicated on days with bong use compared to days with vape use, but used fewer hits on bong use days (Cloutier et al., 2022). But there has been relatively limited focus on cannabis use behavior during higher-risk occasions, such as weekend days when cannabis use is more prevalent (Buckner et al. 2015). Further examinations are warranted for how type and modes of use confer greater risk for cannabis use outcomes in ‘real world’ settings.

The current study is a secondary analysis of daily data (see Linden-Carmichael et al., 2025) among a higher-risk sample of young adult college students who engaged in weekly simultaneous use of alcohol and cannabis. The current study had two aims:1.

To describe the type of cannabis product (plant, concentrates) and individual modes of use (e.g., edibles, joints, vaping) on cannabis use days. We hypothesize that plant use will be the most prevalent type of cannabis product and bong and joint use will be the most prevalent modes of use.

2.

To examine within-individual differences in cannabis use outcomes (i.e., number of hits, negative consequences) by type and mode of cannabis use. We hypothesized that types and modes of use would vary across number of hits and consequences. Specifically, with regard to type of use, days with plant use would be linked with a greater number of hits, but days with concentrate use would be associated with more consequences. With regard to mode of use, days with vape, blunt, or pipe use would be associated with a greater number of hits and bong use would be linked with more consequences.