Alcohol and cannabis co-use in a national sample of U.S. adults ages 30-80

The spreading legalization of cannabis in the U.S. has coincided with increased rates of use in nearly every adult age group (Hasin et al., 2019). In 2020, prevalence of past year cannabis use ranged from 26 % among adults in their early 30 s to 10 % among those ages 50 and older (2021). Given more widespread use of cannabis among adults, it is perhaps not surpring that its co-use with alcohol has increased in recent years (Kepner et al., 2022). There is growing evidence that alcohol and cannabis (AC) co-use can be more problematic than use of either substance alone (Gunn et al., 2022). However, most research has been conducted with young people and it is important to understand the patterns and correlates of AC co-use among adults.

Types of AC co-use include using both substances, but only on separate occasions (concurrent co-use), and using both substances at the same time so their effects overlap (simultaneous co-use). While there is evidence that cannabis can potentially have a substituting or complementing effect on alcohol use (Gunn et al., 2022), generally individuals who engage in AC co-use tend to report heavier and more frequent use than those who use either substance alone (Yurasek et al., 2017). This heavier use, in turn, may contribute to the negative behavioral outcomes associated with AC co-use. Although research on older age groups is lacking, longitudinal studies of young people indicate that AC co-use predicts increased risk of sexual assault (Read et al., 2021), experiencing multiple substance-related problems (e.g., legal, academic, relational, health; Briere et al., 2011), and poorer academic performance (Meda et al., 2017). Cross-sectional studies have found that AC co-use is associated with various risk behaviors such as impaired driving (Duckworth and Lee, 2019, Terry-McElrath et al., 2014), truancy and use of other illicit drugs (Patrick et al., 2018; see also event-level studies by Egan et al., 2019, Gunn et al., 2018, Lee et al., 2020, Linden-Carmichael et al., 2020). While young people who engage in simultaneous AC co-use tend to have a higher risk profile than those who engage in concurrent use only (Cummings et al., 2019), both co-use types are associated with more negative consequences compared to single product use (Jackson et al., 2020, Subbaraman and Kerr, 2015).

Given increasing AC co-use after young adulthood, and its potential for increasing their vulnerability to negative behavioral and health outcomes, it is important to better understand who is at risk for AC co-use during subsequent stages of life. One of the few studies in this area used national data to compare adults ages 50 and older who did versus did not engage in both past month cannabis use and binge drinking (Kepner et al., 2022). Respondents who engaged in co-use were more likely to be younger, male, Black, a tobacco user, and in past-year mental health treatment. While informative, this study is limited by its focus on binge drinking, as well as the use of a comparison group that included both single substance users and abstainers. As a result, virtually nothing is known about AC co-use involving alcohol use in general among adults, or how adults who engage in AC co-use differ from those who use alcohol only. Further, this study was limited to examining individual-level correlates of AC co-use. While important, social-ecological models (e.g., Bronfenbrenner, 1979) emphasize that additional levels of influence, including interpersonal and contextual/environmental factors, should be considered to fully understand complex behaviors such as AC co-use.

Numerous theories have explained the ways in which interpersonal influences on individual behavior may operate through social networks (e.g., Bandura, 1986, Durkheim, 1897/1951, Hirschi, 1969). Studies applying formal social network analysis to understanding alcohol use have found, for example, that problematic alcohol use is more likely among adults with networks that are less resourceful (Shiovitz-Ezra & Litwin, 2012), less diverse (Kim et al., 2018), and denser (Tucker et al., 2021). One of the few studies examining interpersonal factors associated with AC co-use found that young adults were more likely to engage in AC co-use if they had spent more time during adolescence with peers who used one or both substances (D’Amico et al., 2020). Together, this suggests that both network structure (e.g., density) and composition (e.g., presence of substance users) may be relevant to understanding AC co-use among adults.

The study of contextual influences on substance use has often focused on neighborhoods, with social disorganization theories positing that poverty, instability, and lack of cohesion interfere with residents’ ability to form and enforce common social norms and control mechanisms that deter problematic behavior (Sampson et al., 2002). Applied to substance use, studies indicate that younger people who live in disadvantaged neighborhoods are more likely to engage in heavier substance use (Abdelrahman et al., 1999; Karvonen and Rimpela, 1997, Tucker et al., 2013) and specifically that adult cannabis use is linked to neighborhood problems and low social cohesion (Taggart et al., 2018). Our own work has shown that both neighborhood cohesion and disorder are associated with binge drinking among adults ages 30 and older (Tucker et al., 2021). Despite the relevance of neighborhood characteristics to substance use, we are not aware of studies examining whether cohesion and disorder within adults’ neighborhoods are associated with their likelihood of AC co-use.

This study extends the limited literature on adult AC co-use in four important respects. First, it examines the prevalence of simultaneous and concurrent-only AC co-use in a nationally representative sample of U.S. adults ages 30 and older. Second, it extends the Kepner et al. (2022) study by not only examining individual correlates of AC co-use, but also social network and neighborhood characteristics that prior work has suggested are relevant to substance use. Third, given research showing that AC co-use is associated with poorer outcomes among younger people, this study longitudinally examines whether adults who engage in AC co-use are more likely to show escalations in their heaviness of drinking and mental health problems over a two-year period compared to adults who use alcohol only. Little is known about long-term physical effects of AC co-use among adults; as such, we also explore group differences on physical ailments over time. Finally, it examines stability and change in substance use, with a specific focus on the extent to which adults initiate or quit AC co-use over time.

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