What Is Comorbidity?
“Comorbidity” is a term used to describe two or more disorders or illnesses occurring in the same person. They can occur at the same time or one after the other. Comorbidity also implies interactions between the illnesses that can worsen the course of both.
Is Drug Addiction a Mental Illness?
Yes, addiction changes the brain in fundamental ways, disturbing a person’s normal hierarchy of needs and desires and substituting new priorities connected with procuring and using the drug. The resulting compulsive behaviors that weaken the ability to control impulses, despite the consequences, are similar to hallmarks of other mental illnesses.
How Common Are Comorbid Drug Addiction and Other Mental Illnesses?
Many people who are addicted to drugs are also diagnosed with other mental disorders and vice versa. For example, compared with the general population, people addicted to drugs are roughly twice as likely to suffer from mood and anxiety disorders, with the reverse also true.*
Why Do These Disorders Often Co-occur?
Although drug use disorders commonly occur with other mental illnesses, this does not mean that one caused the other, even if one appeared first. In fact, establishing causality or even directionality (i.e., which came first) can be difficult. However, research suggests the following possibilities for their co-occurrence:
- Drug abuse may bring about symptoms of another mental illness. Increased risk of psychosis in some marijuana users suggests this possibility.
- Mental disorders can lead to drug abuse, possibly as a means of “self-medication.” Patients suffering from anxiety or depression may rely on alcohol, tobacco, and other drugs to temporarily alleviate their symptoms.
- These disorders could also be caused by common risk factors, such as—
- Overlapping genetic vulnerabilities. Common genetic factors may make a person susceptible to both addiction and other mental disorders or to having a greater risk of a second disorder once the first appears.
- Overlapping environmental triggers. Stress, trauma (such as physical or sexual abuse), and early exposure to drugs are common factors that can lead to addiction and other mental illnesses.
- Involvement of similar brain regions. Brain systems that respond to reward and stress, for example, are affected by drugs of abuse and may show abnormalities in patients who have certain mental disorders.
- Drug use disorders and other mental illnesses are developmental disorders. That means they often begin in the teen years or even younger—periods when the brain experiences dramatic developmental changes. Early exposure to drugs of abuse may change the brain in ways that increase the risk for mental disorders. Also, early symptoms of a mental disorder may indicate an increased risk for later drug use.
How Are These Comorbid Conditions Diagnosed and Treated?
The rate of comorbidity between drug use disorders and other mental illnesses calls for a comprehensive approach that identifies and evaluates both. Accordingly, anyone seeking help for either drug abuse/addiction or another mental disorder should be checked for both and treated accordingly.
There are several behavioral therapies that have shown promise for treating comorbid conditions. These approaches can be designed to target patients according to specific factors such as age or marital status: some therapies have proved more effective for adolescents, while others have shown greater effectiveness for adults; some therapies are designed for families and groups, others for individuals.
While several medications exist for treating addiction and other mental illnesses, most have not been studied in patients with comorbidities. For example, individuals addicted to heroin, prescription pain medications, cigarettes, or alcohol can be treated with appropriate medications to ease withdrawal symptoms and drug craving; similarly, separate medications are available to help improve the symptoms of depression and anxiety. More research is needed, however, to better understand how such medications act when combined in individuals with comorbidities, or whether such medications can be dually effective for treating comorbid conditions.
Other Information Sources
For more information on comorbidity between drug use disorders and other mental illnesses, see—
National Institute of Mental Health, National Institutes of Health, at www.nimh.nih.gov
* Drug abuse and drug dependence, or addiction, are considered drug use disorders—a subgroup of mental disorders—when they meet the diagnostic criteria delineated in the Diagnostic and Statistical Manual of Mental Disorders (DSM). Drug dependence, as DSM defines it, is synonymous with the term "addiction," which will be used preferentially in this document. Criteria for drug abuse hinge on the harmful consequences of repeated use but do not include compulsive use, tolerance, or withdrawal. Since the focus of this report is on comorbid drug use disorders and other mental illnesses, the terms “mental illness”/“mental disorders” will refer here to disorders other than drug use, such as depression, schizophrenia, anxiety, and mania. The terms “dual diagnosis,” “mentally ill chemical abuser,” and “co-occurrence” are also used to refer to drug use disorders that are comorbid with other mental illnesses.
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