This report identifies significant gaps in the care of individuals with co-occurring substance use and mental health (CoSUM) disorders within UK health systems. People affected by CoSUM disorders – particularly those from vulnerable or marginalised backgrounds, often experience poorer outcomes than individuals with either condition alone, yet they make up a large proportion of those accessing mental health and substance use services.

CoSUM disorders involve various combinations of substances (including alcohol) and mental health conditions (such as affective or psychotic disorders), making assessment and treatment complex. Currently, health services lack the tools to properly identify and respond to the different types and severities of CoSUM disorders, leading to under-identification and insufficient strategic planning.

Mental health services have been known to exclude people from receiving the care they need due to their substance use. However, all mental health services should, as a minimum, assess substance use and refer individuals to appropriate support. In reality, many mental health services are poorly equipped even to provide basic assessments or manage withdrawal, particularly in inpatient settings, which puts patients at considerable risk.

Substance use services, while not expected to treat severe enduring mental illnesses, struggle to support individuals with mild to moderate mental health needs and often lack effective referral pathways for those needing specialist mental healthcare. Concerningly, in some cases, they use mental illness as a reason to deny someone access to substance use treatment.

Collaboration between mental health and substance use services remains minimal, and commissioning structures encourage disjointed care. Across the UK, more integrated and responsive services are urgently needed.