Dual diagnosis

Did You Know?

• The DSM-IV advises that diagnoses of primary psychiatric disorders not be made in the absence of sobriety for up to one year, to allow substance-induced post-acute-withdrawal symptoms to dissipate.
• The COVID-19 pandemic has been associated with increased rates of substance use and psychological distress, potentially increasing co-occurring disorders in vulnerable populations.

Differentiating pre-existing and substance induced

Distinguishing substance-induced psychiatric symptoms from independent mental disorders is a common clinical challenge with important treatment implications. Substance use disorders, including those involving alcohol and prescription medications, can produce symptoms that mimic mental illness, and these often resolve with prolonged abstinence. Psychiatric symptoms may arise during intoxication or withdrawal, and in some cases persist long after detoxification, such as prolonged psychosis or depression following amphetamine or cocaine use.

Hallucinogens can trigger lasting delusional phenomena, while cannabis may induce panic attacks during intoxication or a dysthymia-like state with sustained use. Severe anxiety and depression from sustained alcohol use typically abate with abstinence, though a protracted withdrawal syndrome—most notably from benzodiazepines—can persist for months or years. The similar patterns of comorbidity and risk factors in substance-induced and independent conditions suggest shared underlying etiologic factors.

Prevalence

Dual disorders are very common, with strong associations between mental disorders and substance use disorders. Adolescents and young adults are particularly at risk, as early substance use can interfere with brain development and worsen emerging mental health conditions. In the United States, a 2011 national survey found that 17.5% of adults with a mental illness had a co-occurring substance use disorder, representing 7.98 million people. Canadian estimates are higher, with 40-60% of adults with severe and persistent mental illness experiencing a substance use disorder in their lifetime.

A US study by Kessler and colleagues reported that 47% of clients with schizophrenia had a substance misuse disorder at some point, with significantly higher odds among those with psychotic illness. Among 187 chronically mentally ill patients living in the community, about a third used alcohol, street drugs, or both in the six months before evaluation. UK studies show more moderate rates: one found 7% of individuals with schizophrenia reported problematic drug use in the prior year, and 21% reported it earlier.

In the London borough of Croydon, prevalence of dual diagnosis among psychotic individuals was 33% for any substance use, 20% for alcohol misuse only, and 5% for drug misuse only, with 35% reporting lifetime illicit drug use.

Treatment

Only a small proportion of individuals with co-occurring disorders receive treatment for both conditions; in 2011, an estimated 12.4% of American adults with co-occurring disorders received both mental health and addictions treatment. Clients often face exclusion from mental health services if they disclose substance use, and vice versa. Several treatment approaches exist: partial treatment addresses only the disorder considered primary; sequential treatment stabilizes the primary disorder before treating the secondary; parallel treatment involves separate providers for mental health and addictions.

Integrated treatment blends interventions into a single coherent package with a consistent philosophy, treating both disorders as primary. This approach can improve accessibility, engagement, compliance, mental health symptoms, and overall outcomes. The Substance Abuse and Mental Health Services Administration describes integrated treatment as in the best interests of clients, programs, funders, and systems. Comprehensive integrated programs typically combine pharmacotherapy with psychosocial interventions, continuous assessment, and long-term relapse-prevention support, with service intensity matched to the client's stage of readiness for change.

Theories of dual diagnosis

Several theories explain the relationship between mental illness and substance use. The causality theory proposes that certain substance use may causally lead to mental illness. Strong evidence links cannabis use to psychotic and affective experiences, with more frequent use increasing the risk for psychosis. However, this connection does not prove causation, as rates of schizophrenia have remained relatively stable despite large increases in cannabis consumption over the past 40 years in Western society.

Attention-deficit hyperactivity disorder is present in one in four people with a substance use disorder, complicating treatment. ADHD is associated with increased drug craving, earlier initiation of substance misuse, poorer outcomes, and more psychiatric complications. While stimulant medications generally do not worsen substance use, they are sometimes used non-medically. Psychosocial therapy, nonstimulant medications, and extended-release stimulants are treatment options that reduce these risks.