PROJECT SUMMARY Problematic substance use (SU) is an ongoing epidemic across American Indian and Alaska Native (AIAN) communities, with AIAN people experiencing the highest rates of SU-related morbidity and mortality of any racial/ethnic group. However, AIAN young men have been largely neglected by SU prevention science. There is a lack of prevention strategies supported by science, and specifically designed for AIAN men during the critical time as they transition from adolescents to adulthood. Moreover, no current prevention programming has been designed to leverage contextual (e.g., historical trauma and colonization) and cultural strengths to optimize effectiveness and sustainability. Rich cultural and traditional practices are particularly vital for AI men, yet these practices and worldviews are largely untapped to date. Our team has spent the past two years adapting and piloting the Common Elements Treatment Approach (CETA), an evidence-based, transdiagnostic intervention that can be tailored to meet the unique needs of participants. The proposed study builds on this track record of adapting CETA for Indigenous prevention science, 35+ years of research collaboration between the Johns Hopkins Center for Indigenous Health (CIH; formerly Center for American Indian Health) and the Navajo Nation, and CIH's decades of experience disseminating and scaling evidence-based interventions that have now reached over 150+ AIAN communities. Led by a team of Indigenous researchers and allied co-investigators, and in collaboration with a Community Research Council, our team will collaborate with two rural Navajo communities to adapt CETA and test this adapted version, Hastóí Bidziil (Strong Men), in a randomized controlled trial through the following Aims: Aim 1: Adapt CETA and associated implementation strategies for young AI men, age 18-26 years, resulting in the Hastóí Bidziil (Strong Men) intervention. Hypothesis: Standard delivery of CETA will require modifications for cultural and gendered specific delivery of CETA for maximum community impact. Aim 2: Determine the effectiveness of Hastóí Bidziil for reducing SU among N=160 AI men (ages 18-26) using a randomized controlled trial design. Hypothesis: Hastóí Bidziil will reduce SU among young adult males enrolled in the intervention arm of the randomized controlled trial. Aim 3: Explore mediators and moderators of Hastóí Bidziil, guided by the Indigenist Ecological Systems Model, to inform a precision approach to implementation. Hypothesis: Program effectiveness will be driven by several moderating and mediating factors which will help inform how best to scale, implement, and tailor the program if proven effective. This project synergizes with CIRCLE's aims of advancing Indigenous and allied leadership, understanding heterogeneous patterns of SU to further a precision public health approach to SU prevention, and building on Indigenous sources of strength. Our focus also aligns with recent NIDA funding pri...