Substance use disorders occur when the recurrent use of alcohol and/or drugs causes clinically significant impairment, including health problems, disability, and failure to meet major responsibilities at work, school, or home.

The coexistence of both a mental health and a substance use disorder is referred to as co-occurring disorders. The National Institute for Mental Health’s Mental Health Information Substance Use and Mental Health page reads:

Did you know that addiction to drugs or alcohol is a mental illness? Substance use disorder changes normal desires and priorities. It changes normal behaviors and interferes with the ability to work, go to school, and to have good relationships with friends and family. In 2014, 20.2 million adults in the U.S. had a substance use disorder and 7.9 million had both a substance use disorder and another mental illness. More than half of the people with both a substance use disorder and another mental illness were men (4.1 million). Having two illnesses at the same time is known as “comorbidity” and it can make treating each disorder more difficult.

Although substance 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 three possibilities for this common co-occurrence:

Common risk factors can contribute to both mental illness and substance use disorders. Research suggests that there are many genes that can contribute to the risk of developing both a substance use disorder and a mental illness. For example, some people have a specific gene that can make them at increased risk of mental illness as an adult, if they frequently used marijuana as a child. A gene can also influence how a person responds to a drug – whether or not using the drug makes them feel good. Environmental factors, such as stress or trauma, can cause genetic changes that are passed down through generations and may contribute to the development of mental illnesses or a substance use disorder.

Mental illnesses can contribute to drug use and substance use disorders. Some mental health conditions have been identified as risk factors for developing a substance use disorder. For example, some research suggests that people with mental illness may use drugs or alcohol as a form of self-medication. Although some drugs may help with mental illness symptoms, sometimes this can also make the symptoms worse. Additionally, when a person develops a mental illness, brain changes may enhance the rewarding effects of substances, predisposing the person to continue using the substance.

Substance use and addiction can contribute to the development of mental illness. Substance use may change the brain in ways that make a person more likely to develop a mental illness.

Additional Information

NIDA is the reference for information on this page. More information about Co-Occurring Disorders, including diagnosis, treatment and support resources, can be found on the NIDA website at www.drugabuse.gov/publications/drugfacts/comorbidity-substance-use-disorders-other-mental-illnesses.

If you or a family member is experiencing a mental health or an alcohol or other drug-related emergency, seek immediate assistance by calling the 24-hour Suicide Prevention, Mental Health/Addiction Crisis, Information and Referral Hotline: (216) 623-6888 or United Way 2-1-1. You can also text '4hope' to 741-741.