Alcohol and cannabis use among young adults remain public health concerns in the U.S. Estimates in 2022 from the Monitoring the Future study show 67.5 % of young adults 19 to 30 reporting past 30-day alcohol use and 30.5 % reporting past two-week binge drinking (i.e., 5 + drinks in a row), and 28.8 % reporting past 30-day cannabis use and 11.3 % reporting daily use—a doubling since 2012 (Patrick et al., 2023). The past decade has also brought heightened concerns about young adults’ emotional health with national studies showing significant increases in prevalence of major depressive disorder and suicidal ideation (Ivey-Stephenson et al., 2022, Twenge et al., 2019).

Depressive symptoms frequently co-occur with substance use and substance use disorders, including alcohol and cannabis use (Hasin et al., 2016, Lu et al., 2022). To understand this co-occurrence, there has been substantial interest in self-medication and affect-regulation models (e.g., McCabe et al., 2023) that suggest that people with elevated depressive symptoms may use alcohol or cannabis as a coping strategy. Some research suggests that depressive symptoms are longitudinally associated with substance use (Bolanis et al., 2020, Mushquash et al., 2013, Rhew et al., 2017), although findings are inconsistent (e.g., Bierhoff et al., 2019). Despite these mixed findings, national data from 12th grade students suggests that the prevalence of coping reasons for cannabis use has increased (Patrick et al., 2024).

Mutual maintenance theories suggest that mental health symptoms and substance use may be mutually reinforcing (Stewart et al., 2014). As substance use continues in response to distress, this could lead to increasing regularity of use through negative reinforcement. Increased use could also lead to subsequent tolerance and withdrawal, which can yield negative affect and symptoms of depression, and continued substance use, to reduce negative feelings. These feedback loops could lead to sustained and possible escalations in depressive symptoms and substance use over the long-term. Consistent with this, studies suggest that coping reasons are associated with more problematic use (Colder et al., 2019, Patrick et al., 2011).

As an approach to test mutual maintenance, studies could use intensive longitudinal data with repeated measures of substance use behaviors and depressive symptoms to identify individuals showing patterns of greater substance use during times (e.g., months, days) of increased depressive symptoms, and then link these person-specific patterns to distal long-term outcomes. For example, one study of college students used a two-stage approach where, first, daily data from multiple 14-day bursts and multilevel modeling were used to estimate each participant’s unique slope for their average daily association between stress and likelihood of alcohol use, and, second, the person-specific extracted slopes were used to predict alcohol-related problems reported on a later follow-up survey (Russell et al., 2017). This study found that those who showed greater likelihood of alcohol use on high versus low stress days reported more alcohol use problems during their fourth year of college.

As a test of mutual maintenance, this study examined whether person-specific patterns of monthly associations of depressive symptoms with alcohol and cannabis use were associated with longer-term hazardous alcohol and cannabis use (a pattern of use associated with adverse health and social outcomes) and depressive symptoms. This study utilized two forms of data from a prospective study of 778 young adults ages 18–25: 1) data collected monthly for 24 consecutive months, and 2) data from a follow-up survey 30 months after baseline to assess distal outcomes. We hypothesized that those participants exhibiting stronger monthly associations of depressive symptoms with alcohol or cannabis use during the first 24 months would have higher levels of hazardous drinking or cannabis use, respectively, and higher levels of depressive symptoms at the 30-month follow-up.