Revised March 2011
What Is Comorbidity?
The term “comorbidity” describes 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 negative 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 which came first or why can be difficult. However, research suggests the following possibilities for this common co-occurrence:
- Drug abuse may bring about symptoms of another mental illness. Increased risk of psychosis in vulnerable 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 shared risk factors, such as—
- Overlapping genetic vulnerabilities. Predisposing 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 environmental 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 with 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 high 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.
Several behavioral therapies have shown promise for treating comorbid conditions. These approaches can be tailored to patients according to age, specific drug abused, and other factors. Some therapies have proven more effective for adolescents, while others have shown greater effectiveness for adults; some are designed for families and groups, others for individuals.
Effective medications exist for treating opioid, alcohol, and nicotine addiction and for alleviating the symptoms of many other mental disorders, yet most have not been well studied in comorbid populations. Some medications may benefit multiple problems. For example, evidence suggests that bupropion (trade names: Wellbutrin, Zyban), approved for treating depression and nicotine dependence, might also help reduce craving and use of the drug methamphetamine. More research is needed, however, to better understand how these medications work, particularly when combined in patients with comorbidities.
Other Information Sources
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Introduces a report that focuses on the topic of comorbid drug use disorders and other mental illnesses, a research priority for NIDA.