More than 3.5 million young people ages 14 through 25 in the United States experience some form of homelessness annually (Morton et al., 2018). Youth experiencing homelessness (YEH) are often more likely to experience a range of behavioral and psychosocial health-risk factors and vulnerabilities than youth who are housed (Heerde et al., 2020, Morton et al., 2018, Whitbeck, 2009). As an example, YEH engage in substance use at significantly higher rates than their housed counterparts (Nyamathi et al., 2012, Santa Maria et al., 2018, Wenzel et al., 2010). In a sample of 1,426 YEH, one study found that 60.7% use marijuana, 34% alcohol, 28.0% synthetic marijuana, 17.7% cocaine, 17.5% methamphetamines, 15.4% ecstasy, 9.3% heroin, 8.3% injection drugs, and 8.2% crack (Chassman et al., 2022). While tobacco, alcohol, and marijuana are among the most used substances (Glasser et al., 2022, Shadel et al., 2015, Wenzel et al., 2010), illicit substances such as cocaine, crack, and methamphetamine, are also a cause for concern among YEH (Barman-Adhikari et al., 2018). Substance use among YEH is influenced by a multitude of factors. These determinants encompass both individual and environmental factors (see Fig. 1).

For example, experiences of childhood trauma, including abuse and neglect, are common among this population; approximately 84% of YEH have experienced either physical or sexual abuse prior to becoming homeless, and approximately 42% have experienced both (Bender et al., 2015). Moreover, YEH are exposed to higher rates of sexual violence and assault after they leave home (Bender et al., 2015). A 2018 study conducted by Pedersen et al., which focused on service utilization, found that one-third to half of their research participants (n = 273) met criteria for behavioral health problems such as substance use disorder (30%), PTSD (39%), and depression (47%). Furthermore, the harsh conditions of street environments and unstable shelter further exacerbate the issue of substance use among YEH. Sleeping outdoors and engaging in illicit income generation, such as survival sex, are dangerous means of survival that increase the risk of substance use (Santa Maria et al., 2018, Thompson et al., 2015; Tyler & Schmitz, 2020).

The prevalence of substance use varies among youth experiencing homelessness, with differences observed based on sociodemographic characteristics. For example, research suggests that substance use in this population is associated with age (DiGuiseppi et al., 2020, Johnson and Chamberlain, 2008, Nyamathi et al., 2012, Patterson et al., 2012, Santa Maria et al., 2018, Tompsett et al., 2013), race and ethnicity (Bousman et al., 2005, Combs et al., 2020, Nyamathi et al., 2012, Rice et al., 2011, Santa Maria et al., 2018), sexual orientation (Combs et al., 2020, DiGuiseppi et al., 2020, Maria et al., 2020, Salomonsen-Sautel et al., 2008, Santa Maria et al., 2018), gender identity (Hadland et al., 2011, Hathazi et al., 2009), and region (Ferguson et al., 2010, Santa Maria et al., 2018).

Research suggests that a greater proportion of older YEH engage in the use of multiple substances, or polysubstance use, compared to their younger counterparts (Greene et al., 1997, Milburn et al., 2017, Nyamathi et al., 2012, Salomonsen-Sautel et al., 2008). In addition, older YEH are more likely to use illicit substances, such as heroin and cocaine, whereas younger YEH are more likely to binge drink (Edidin et al., 2012, Harford et al., 2018). The relationship between substance use and race/ethnicity in the context of YEH presents somewhat inconsistent findings. For instance, Zhang & Slesnick (2018) reported that among their sample of 273 YEH, 65.5% of Black YEH exhibited poorer outcomes related to substance use and social stability compared to other racial groups. In contrast, a study analyzing cross-sectional data from 1,010 YEH accessing services at three drop-in agencies in Los Angeles found that Black YEH reported lower levels of binge drinking and reduced usage of hard drugs, injection drugs, and prescription drugs in comparison to their White counterparts (Combs et al., 2020). These variations warrant further examination to gain a comprehensive understanding of the complex interplay between race/ethnicity and substance use within the YEH population. Research has also found that gender identity and sexual orientation may influence substance use, with females and youth identifying as heterosexual less likely to use substances compared to their male or LGBQ counterparts (Hadland et al., 2011, Hathazi et al., 2009, Santa Maria et al., 2018). In addition, substance use among YEH has been found to vary depending on region. Characteristics, such as the prevalence of substance use in the general population, availability of homelessness services, and mobility may contribute to differences in substance use in specific cities in the United States (Ferguson et al., 2010).

Substance use often co-occurs with mental health, trauma, and sexual risk behaviors. For example, YEH who use substances also report high rates of reduced emotional wellbeing, low self-esteem, and mental health diagnoses (Maria et al., 2020, Rhoades et al., 2014). In addition, YEH with high sexual risk behaviors, compared to those with low sexual risk behaviors, have been shown to engage in higher rates of substance use as well as experience greater childhood adversities (Maria et al., 2020). Notably, high rates of substance use among YEH are associated with longer duration of homelessness (Gomez et al., 2010, Johnson and Chamberlain, 2008, Lightfoot et al., 2018, Thompson et al., 2015), lower education (Bender, Yang, et al., 2015; Combs et al., 2020), and a history of foster care (Bender, Yang, et al., 2015; Berzin et al., 2011, Combs et al., 2020, Nyamathi et al., 2012).

To date, most of the research documenting the relationship between substance use and sociodemographic and health-risk factors among YEH have used variable-centered approaches. Because these approaches examine relationships among variables, as opposed to identifying subgroups of individuals based on shared characteristics, they may be limited in their ability to understand more complex patterns of substance use among this population (Shi et al., 2020). Indeed, person-centered analyses, such as latent class analysis (LCA), allow for the classification of individuals into mutually exclusive classes based on their similarities on a set of constructs.

Importantly, a growing body of research suggests that individuals can be classified into distinct groups according to their substance use (DiGuiseppi et al., 2020; Morean et al., 2017; Wu et al., 2020). For example, in a study among high school students in Connecticut, Morean et al., (2017) revealed four distinct classes: one characterized by primarily abstaining from substance use, another featuring e-cigarette and alcohol use as dominant, a third exhibiting primary use of marijuana and alcohol, and a fourth marked by the primary use of all available products. Similarly, in a study of youth in Arizona, Wu et al., (2020) identified a five-group model: (1) Serious Users, (2) Moderate Users, (3) Non-progressive Users, (4) Common Substance Users, (5) Abstainers.

Among YEH, DiGuiseppi et al. (2020) surveyed 1,032 YEH and identified five classes of YEH according to their substance use histories. These classes included: heavy alcohol and marijuana; illicit drug use; high all polysubstance use; primarily marijuana; and low use (DiGuiseppi et al., 2020).

These results highlight the importance of investigating patterns of substance use, such that there may be unique combinations of substances that relate to the needs of these youth, which may, in turn, better inform future targets for prevention and intervention. Yet, there is limited research focused on polysubstance use among YEH according to class membership as well as the linkage to sociodemographic and health-risk characteristics.

The current study sought to expand upon the existing research on substance use among YEH, incorporating findings from the DiGuiseppi et al. (2020) study. This research uniquely focuses on a geographically diverse sample of YEH drawn from seven cities across the United States. By utilizing a mixture modeling approach, the study aimed to quantitatively assess the prevalence of polysubstance use within this specific population. Specifically, we employed LCA to identify subgroups of YEH according to their substance use. Next, we conducted multinomial logistic regression analyses to identify sociodemographic and health-risk characteristics associated with substance use class membership. Our hypotheses were rooted in the literature review, suggesting that the various polysubstance use classes would have been associated with a wider array of health-risk factors and sociodemographic characteristics.