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When an individual has two or more distinct illnesses at the same time, this is called comorbidity. The ailments could be physical or mental. For example, a person might suffer from depression and multiple sclerosis, or anxiety and an eating disorder.

Disease overlap is common. Historically, 80 percent of Medicare spending covers patients with four or more concurrent conditions. Multiple disorders can exacerbate one another and make treatment a longer process or more difficult to achieve.

Understanding Comorbidity
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Many different mental health disorders can co-occur. One common example is depression and anxiety. However, some researchers argue that the two have similar roots and therefore do not constitute distinct disorders. Nonetheless, depression commonly overlaps with other disorders as well, such as bipolar disorder and ADHD.

Why is there debate over the term comorbidity?

There is debate over the definition of comorbidity, such as whether the term encompasses overlap between two conditions of any kind or between one medical and one psychiatric, as well as the relationship between the two, such as whether to distinguish between primary and secondary conditions.

What is psychiatric comorbidity?

Psychiatric comorbidity means that there is the coexistence of multiple psychiatric disorders. For example, a person with schizophrenia may also suffer from any of these disorders: panic, PTSD, OCD, generalized anxiety, social anxiety.

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Substance Use and Comorbidities
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The combination of substance use disorders and other mental illnesses is widespread. Half of the people who experience a mental illness will also be diagnosed with a substance use disorder at some point in their lives, according to the National Institute on Drug Abuse. The same goes for those first diagnosed with a substance use disorder and later a mental illness. In 2018, 9.2 million Americans had both a substance use disorder and a mental illness, according to the National Survey on Drug Use and Health.

What comes first, a substance use disorder or mental illness?

A person can be first diagnosed with either a substance use disorder or a mental illness. Sometimes they occur concurrently, or they can occur one after the other.

What do co-occurring disorders and dual diagnosis mean?

Co-occurring disorders and dual diagnosis are two related terms. The term co-occurring disorders refers to when an individual has a substance abuse disorder and a mental illness at the same time, such as schizophrenia or depression. The term dual diagnosis describes the same condition.

The Treatment of Comorbidities
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Treatment should center around all the presenting conditions, rather than treating one in isolation. Successful treatment may leverage medications, such as buprenorphine, and behavioral therapies, such as cognitive-behavioral therapy or dialectical behavior therapy.

Continuing research on the relationship between different diseases is critical to developing the most effective treatment approaches. On an individual level, disclosing multiple disorders to a physician is key to achieving successful care.

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