RIA expert Summary

Substance Abuse and Mental Illness

Published May 31, 2016 This content is archived.

Are people with mental illness more likely to abuse drugs? Or does abusing drugs contribute to mental illness?

This is the “chicken or the egg” question faced by many professionals who treat people with the dual diagnosis of addiction and mental illness. There is no easy answer. The two issues can be intertwined for many reasons. However, understanding the nature of dual diagnosis is key in ensuring patients receive the proper treatment.

The American Psychiatric Association defines a number of mental disorders, including substance-related and addictive disorders, in its Diagnostic and Statistical Manual of Mental Disorders, which is considered the authority for the classification and diagnosis of mental illnesses and conditions.

Mental health disorders exist along a broad spectrum of conditions and symptoms. The most common mental health disorders are anxiety and depression. These disorders impair day-to-day functioning, and are more severe and last longer than the feelings of anxiousness and sadness that everyone experiences. Less common, but more severe mental illnesses include bipolar disorder, schizophrenia and trauma-related disorders such as PTSD. Treatment for mental disorders can include psychotherapy, support services and/or medication, depending on the specific disorder and its severity.

According to the National Institute on Drug Abuse (NIDA), as many as six in 10 people who have a substance use disorder also experience a mental disorder at some point in their lifetime. Within the field of psychiatry, when two or more disorders coexist in the same person, they are referred to as “co-occurring” or “comorbid.”

Why is there a high level of co-occurrence?


A variety of factors account for the high level of co-occurrence of substance use and mental disorders. The “chicken or the egg” issue is part of the problem—drug abuse may initiate the onset or increase the severity of other mental illnesses, or mental disorders may lead to drug use and abuse, as people attempt to “self-medicate” to cope with their symptoms.

Other issues that influence risk for co-occurrence include:

  • Genetic factors
  • Involvement of similar regions of the brain
  • Prenatal drug or alcohol exposure, or the use of illicit substances at an early age
  • Lifetime stresses such as physical or sexual abuse, exposure to violence or other personal trauma

Genetics, neurological factors and stress

People have long believed certain mental illnesses or substance use disorders “run in the family.” Researchers are finding increasing evidence indicating that genetic factors are, in fact, an important cause of this familial pattern predisposing particular people to psychiatric problems, substance abuse or both.

Recent research suggests that roughly 50 percent of a person’s vulnerability to addiction is attributable to genetics, according to NIDA. Genetics also contribute to mental illness. A 2013 study by the National Institute on Mental Illness (NIMH) found that five mental disorders—autism, ADHD, bipolar disorder, major depression and schizophrenia—shared a number of common genes. Many of these genetic vulnerabilities also are related to addiction and may influence the co-occurrence of these disorders.

Researchers also are examining neurotransmitters in the brain and their involvement in both addiction and psychiatric disorders. For example, the neurotransmitter dopamine plays a role in how the brain is affected by addictive substances, as well as in the development of certain mental illnesses such as depression and schizophrenia.  

Children exposed to drugs, alcohol or tobacco in the womb exhibit neurological changes that can increase the risk for behavioral issues, mental health issues and addiction. In a similar fashion, early use of substances can contribute to neurological changes which then influence continued use.

Environmental factors, including stress, also are shared risks that can contribute to the predisposition to substance use disorders, mental illness or both. Individuals who have experienced physical or psychological trauma in youth or adulthood may turn to substance use as a coping mechanism, or trauma may trigger mental illness in people who already have genetic vulnerabilities.


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