What Are Co-Occurring Disorders?

Addiction to drugs or alcohol is a long-lasting and often recurring medical condition; a “substance use disorder” that’s characterized by compulsive use of substances despite devastating consequences.1

Co-Occurring Disorders

When more than one illness occurs in an individual each is said to “co-occur” with the other, implying an interaction between the illnesses that may make one or both worse.2 For example, someone with a history of injecting heroin might have a co-occurring illness like HIV or hepatitis C.

girl going through the effects of having a co occurring disorder

When another mental health condition exists alongside a substance use disorder, it is considered a “co-occurring disorder.” This is actually quite common; in 2018, an estimated 9.2 million adults aged 18 or older had both a mental illness and at least one substance use disorder in the past year, according to the National Survey on Drug Use and Mental Health.3

The American Society of Addiction Medicine defines addiction as a “chronic medical disease involving complex interactions among brain circuits, genetics, the environment and an individual’s life experiences.”4 Interactions between these factors are also involved in other mental health disorders, so it’s not surprising that there’s a high rate of co-occurrence.

Common Co-Occurring Disorders

There are a handful of mental illnesses which are commonly seen with or are associated with substance abuse. These include:5

Eating disorders (specifically anorexia nervosa, bulimia nervosa and binge eating disorder) also occur more frequently with substance use disorders vs. the general population, and bulimic behaviors of binge eating, purging and laxative use are most common.6 In fact, bulimics commonly exhibit multiple drug use disorders and have high rates of alcoholism.7

Co-Occurring Disorders and Substance Abuse: Risk Factors

The high rates of substance abuse and mental illness occurring together doesn’t mean that one caused the other, or vice versa, even if one came first.8 The relationship and interaction between both are complex and it’s difficult to disentangle the overlapping symptoms of drug addiction and other mental illness.

There are common risk factors that contribute both to the development of a mental illness as well as substance use and addition:8

  • Genetic vulnerabilities and epigenetic influences: Genes that influence the action of brain chemicals that carry messages from one neuron to another (i.e., neurotransmitters), such as dopamine and serotonin, can be affected by drugs and commonly dysregulated in mental illness. A person’s environment, such as one that causes chronic stress, or even diet can interact with genetic vulnerabilities or biological mechanisms that trigger the development of mood disorders or addiction-related behaviors.8
  • Brain region involvement: Addictive substances and mental illnesses affect similar areas of the brain and each may alter one or more of the multiple neurotransmitter systems implicated in substance use disorders and other mental health conditions.8
  • Stress: Higher levels of stress may lead to decreased behavioral control and impulsivity that may contribute to mental health issues or the development of substance use.8
  • Trauma and adverse childhood experiences: Post-traumatic stress from war or physical/emotional abuse during childhood puts a person at higher risk for drug use and makes recovery from a substance use disorder more difficult.8

In some cases, a mental health condition can directly contribute to substance use and addiction. Drugs may temporarily reduce symptoms of a mental illness, but they can also make mental health issues worse—cocaine, for example, may worsen symptoms of bipolar disorder and contribute to its progression.8

Finally, substance use may contribute to developing a mental illness by affecting parts of the brain disrupted in the same way as other mental disorders, such as anxiety, mood, or impulse control disoders.8

Co-Occurring Disorders Treatment

Over the last several years, an integrated treatment model has become the preferred model for treating substance abuse that co-occurs with another mental health disorder(s).9

Individuals in treatment for substance abuse who have a co-occurring mental illness demonstrate poorer adherence to treatment and higher rates of dropout than those without another mental health condition.10

Integrated treatment typically involves cognitive behavioral therapy, which boosts interpersonal and coping skills, as well as approaches that help to maintain motivation and support a functional recovery.10

Where evidence has shown medications to be helpful (e.g., for treating opioid or alcohol use disorders), it should be used, along with any medications supporting the treatment or management of mental health conditions.10

Although medications may help, it is only through therapy that individuals can make tangible strides toward sobriety and restoring a sense of balance and stable mental health to their lives.


  1. Diagnostic and statistical manual of mental disorders: DSM-5. (5th ed.). (2013). Washington, D.C.: American Psychiatric Association.
  2. National Institute on Drug Abuse. (2018). Comorbidity: Substance Use Disorders and Other Mental Illnesses.
  3. Center for Behavioral Health Statistics and Quality. (2019). Results from the 2018 National Survey on Drug Use and Health: Detailed Tables. Substance Abuse and Mental Health Services Administration, Rockville, MD.
  4. American Society of Addiction Medicine. (2019). Definition of Addiction.
  5. National Institute on Drug Abuse. (2018). Part 1: The Connection Between Substance Use Disorders and Mental Illness.
  6. National Institute on Drug Abuse. (2018). Why is there comorbidity between substance use disorders and mental illnesses?
  7. Killeen, T., Brewerton, T. D., Campbell, A., Cohen, L. R., & Hien, D. A. (2015). Exploring the relationship between eating disorder symptoms and substance use severity in women with comorbid PTSD and substance use disorders. The American Journal of Drug and Alcohol Abuse, 41(6), 547–552.
  8. National Institute on Alcohol Abuse and Alcoholism. (1991). Alcoholism and Co-occurring Disorders.
  9. Substance Abuse and Mental Health Services Administration. (2013). TIP 42: Substance Abuse Treatment for Persons with Co-Occurring Disorders.
  10. National Institute on Drug Abuse. (2018). What are the treatments for comorbid substance use disorder and mental health conditions?
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