Last update:
05-Jul-2026

The terms co-occurring substance use disorder and mental health disorder, or comorbidity or dual diagnosis refer to the co-existence of a primary mental health disorder with a substance use disorder and not conditions due to intoxication or withdrawal states. It is reported that 35% to 56% of people with a mental health disorder also have a substance use disorder depending on the country and the population. Similarly, it is reported that about 37% of people with alcohol use disorder and about 53% of people with other substance use disorder also have a mental health disorder. The impact of comorbidity on individuals, society, and healthcare systems is significant. Individuals with comorbidity are facing double stigma associated with both conditions and have worse treatment outcomes. The etiology of comorbidity is complex. Evidence supports mostly a correlation rather than a causal relationship. It is proposed that one disorder could lead to the development of the other or that both disorders share the same predisposing factors, either genetic, or biological or social and environmental. Whatever the etiology might be, comorbidity seems to be the rule rather than the exception. Therefore, all health care services, either those for physical health, mental health or substance use disorders, should offer assessment for comorbid disorders and facilitate access to treatment for people with co-occurring substance use and mental health disorders and reduce access barriers and stigma.

Key words: Co-occurring disorders, Dual diagnosis, Mental health, Substance use disorders.