Substance use disorders (SUDs) present a challenge in the emergency department (ED) setting. This article provides an overview of SUDs, their clinical assessment, legal considerations in drug testing, diagnosis, and treatment approaches. SUDs are prevalent and coexist with mental health disorders, necessitating comprehensive evaluation and management. Clinical assessment involves screening tools, substance use history, and identification of comorbidities. Diagnosis relies on a thorough evaluation of substance abuse patterns and associated medical conditions. Treatment approaches encompass a multidisciplinary approach, incorporating counseling, medications, and social support. Effective management of SUDs in the ED requires a comprehensive understanding of these complex disorders.