The high rate of comorbidity between drug use disorders and other mental illnesses highlights the need for an integrated approach to intervention that identifies and evaluates each disorder concurrently and provides treatment as appropriate for each patient’s particular constellation of disorders.80,81 Enhanced understanding of the common genetic, neural, and environmental substrates of these disorders can lead to improved treatments for individuals with comorbidities and may help diminish the social stigma that makes some patients reluctant to seek the treatment they need.
The diagnosis and treatment of comorbid substance use disorders and mental illness are complex, because it is often difficult to disentangle overlapping symptoms.2,80,81 Comprehensive assessment tools should be used to reduce the chance of a missed diagnosis.81 Patients who have both a drug use disorder and another mental illness often exhibit symptoms that are more persistent, severe, and resistant to treatment compared with patients who have either disorder alone.3,82
Patients entering treatment for psychiatric illnesses should be screened for substance use disorders and vice versa. Accurate diagnosis is complicated, however, by the similarities between drug-related symptoms, such as withdrawal, and those of potentially comorbid mental disorders. Thus, when people who use drugs enter treatment, it may be necessary to observe them after a period of abstinence to distinguish between the effects of substance intoxication or withdrawal and the symptoms of comorbid mental disorders. This practice results in more accurate diagnoses and allows for better-targeted treatment.80,81
Polysubstance Use and Comorbid Substance Use Disorders
Polysubstance use is common, and many people develop multiple comorbid substance use disorders (Table 1). For example, among people with a heroin use disorder over 66 percent are dependent on nicotine, nearly 25 percent have an alcohol use disorder, and over 20 percent have a cocaine use disorder. Among people with a cocaine use disorder nearly 60 percent have an alcohol use disorder, approximately 48 percent are dependent on nicotine, and over 21 percent have a marijuana use disorder. As with single-substance use disorders, the diagnosis and treatment of comorbid substance use disorders and mental illness are complex. The use of multiple substances can further complicate diagnosis and treatment.
|Among individuals with:||Percentage of individuals who also have:|
|Alcohol Use Disorder||Nicotine Dependence||Marijuana Use Disorder||Cocaine Use Disorder||Prescription Opioid Use Disorder||Heroin Use Disorder|
|Alcohol Use Disorder||-||23.8||9.5||3.3||3.9||0.9|
|Marijuana Use Disorder||38.7||32.6||-||4.8||7.9||1.8|
|Cocaine Use Disorder||59.8||47.7||21.3||-||16.4||13.4|
|Prescription Opioid Use Disorder||35.2||45.4||17.6||8.2||-||11.2|
|Heroin Use Disorder||24.5||66.3||12.3||20.9||34.9||-|