This section examines the reciprocal and multifaceted relationship between substance use disorders and mental health. Substance use can lead to mental health issues such as depression, anxiety, and psychosis, while existing psychiatric conditions may also predispose individuals to substance use. Adolescents, individuals from low socioeconomic backgrounds, those with severe mental disorders, and people with limited social support are particularly at risk. Stigma, social exclusion, and inadequate access to services further exacerbate these challenges. Among individuals with substance dependence, suicide, anger, low self-esteem, and social isolation are commonly observed, complicating treatment processes. In this context, the multidimensional roles of nurses such as assessment, withdrawal management, psychoeducation, counseling, psychosocial support, and advocacy are emphasized. Nursing practices based on empathy and a nonjudgmental approach not only enhance adherence to treatment but also contribute to the reintegration of individuals into society. Effective intervention requires interdisciplinary, holistic, and community-based approaches.