A person’s emotional, psychological, and social wellbeing, influencing how individuals think, feel, behave, and cope with life’s challenges. In the context of substance use disorders, mental health is closely interconnected with patterns of substance use, as mental health conditions can increase vulnerability to substance misuse and substance use can also affect mental wellbeing. Addressing mental health alongside substance use is therefore essential for effective prevention, treatment, and recovery, often requiring integrated, person-centred approaches that support overall wellbeing and functioning.