A Systematized Review of Traumatic Stress and Substance Use Interventions in Young Adults: Implications for Intervention Development with Young Adults Experiencing Homelessness.

Young adults experiencing homelessness (YEH; aged 18-25) face high rates of co-occurring trauma and substance use problems. Trauma, homelessness, and substance use exacerbate one another, leading to a cycle that prolongs homelessness and negatively impacts health outcomes. Despite clear links between trauma, homelessness, and substance use, no intervention to date has effectively interrupted the cycle for YEH. This study used a systematized review to characterize existing interventions addressing traumatic stress and substance use to identify potentially adaptable components, implementation strategies, and structural features across the broader young adult intervention literature that could inform the development of a novel, integrated intervention for YEH. A systematized review of peer-reviewed studies from PsycINFO and PubMed was conducted. Searches captured domains of young adulthood, interventions, substance use, and traumatic stress, with and without homelessness terms. A total of 2,100 titles were screened; after duplicate removal and multi-stage screening, 39 studies met inclusion criteria. Data were extracted using a structured coding framework across three domains: effectiveness, real-world implementation, and intervention characteristics. Over half of studies used randomized controlled designs, and about three-quarters reported significant improvements across multiple outcomes (e.g., substance use, traumatic stress, mental health). However, very few interventions concurrently targeted traumatic stress and substance use, and none were designed specifically for YEH. Implementation findings highlighted strong retention but limited reporting on fidelity and cost. Interventions were most commonly delivered in academic, clinical, or service settings, with wide variation in duration, modality, and theoretical orientation. In 16 studies, at least half of participants experienced homelessness/housing instability. Although no single intervention was directly adaptable for YEH, the review identified key components to inform intervention development, including brief, flexible delivery; harm-reduction approaches; and feasibility within community-based service settings. These findings represent a critical pre-implementation step and may inform the development of a novel integrated traumatic stress and substance use intervention tailored to the needs and constraints of YEH. Future research should prioritize intervention testing directly within YEH populations to determine which components retain effectiveness and feasibility in the context of homelessness.