Substance use disorders (SUDs) and mental health disorders frequently co-occur, presenting complex challenges for diagnosis, treatment, and recovery. This comprehensive review explores the intricate relationship between SUDs and mental health, highlighting the bidirectional influences, shared risk factors, and integrated treatment approaches. Understanding the intersection of these disorders is crucial for healthcare providers to deliver comprehensive and effective care. This article discusses the epidemiology of co-occurring SUDs and mental health disorders, examines underlying mechanisms, and outlines evidence-based strategies for integrated care.