Research has shown that there is a strong link between substance use and mental health disorders. It is estimated that over half of those who develop a substance use disorder will also experience mental illness over the course of their lives1.  When a substance use disorder and mental health disorder occur in the same individual, simultaneously or consecutively, they are described as having a co-occurring disorder.

Due the high rate of co-occurrence between SUD and mental illness, there has been a strong focus on understanding the relationship between the two in order to provide an appropriate diagnosis and treatment plan. Establishing which disorder appeared first, or whether one disorder caused the other, is often difficult for clinicians to determine for a variety of reasons. For someone experiencing a co-occurring disorder, it is imperative to receive appropriate treatment to have a successful recovery. An integrated treatment approach has been shown to improve recovery rates for individuals with a co-occurring diagnosis2.

What Causes a Co-Occurring Disorder?

Figuring out which disorder came first or whether or not one caused the other is not as clear cut as many might expect. Therefore, the relationship between substance use and mental health disorders is often understood by examining common risk factors and learning about how one disorder can influence the other. Both disorders are generally believed to be caused by similar issues related to genetics or exposure to trauma early in life3. Common risk factors include3:


While there is no single gene that can predict whether someone will develop a SUD or another mental illness, research has identified several genes that contribute to the development of both disorders. It is estimated that 40 to 60 percent of a person’s vulnerability to a SUD can be attributed to genetic factors.  Additionally, studies have shown that when environmental risk factors interact with genetic vulnerability during key developmental life stages there is an increased likelihood for both mental illness and substance use disorders.

Environmental Factors

Multiple environmental influences have been linked to an increased risk for the development of both disorders.  These include chronic stress and exposure to adverse childhood experiences. Early life stress and chronic stress can lead to brain changes that are thought to underlie the link between the disease processes of both substance use and mental health disorders.  Additionally, research has made clear that physically or emotionally traumatized individuals are at a much higher risk for developing SUD’s.

There is also evidence that indicates substance use disorders and mental illnesses can contribute to the development of the eachother3.  In some instances, substance use can lead to the onset of one or more symptoms of another mental illness by inducing changes in the brain structure that ignite an underlying predisposition for mental illness3.  Similarly, individuals with a mental health disorder may begin to use substances as a form of self-medication, ultimately worsening the symptoms of their mental illness in the long run3.

Why are Co-Occurring Disorders Often Overlooked?

Substance use disorders and mental illness often have many overlapping symptoms.  Diagnosing a co-occurring disorder can prove tricky as it is difficult to disentangle the reported and observable symptoms.  It is not uncommon for someone with a co-occurring disorder to only access treatment for one disorder, while the other remains untreated.  Lack of appropriate screening and evaluation also leads to misdiagnosis or inappropriate treatment recommendations.  Providing integrated evaluations and treatment services is crucial in helping those with co-occurring disorders achieve lasting recovery.

Treatment for Co-Occurring Disorders

Research suggests that when co-occurring conditions are present an integrated treatment approach results in the best outcome4. This means that both the SUD and mental illness are treated in the same time and ideally at the same place.  An integrated treatment approach often includes medication management, behavioral therapies, and other support services to address the comprehensive needs of the individual.

If you or a loved one is struggling with a co-occurring disorder, contact Greenbriar Treatment Center today.  As a Co-Occurring Capable treatment provider, Greenbriar is equipped to help you determine the most appropriate level of care and help you achieve your recovery goals. 

  1. NIDA. 2021, April 13. Part 1: The Connection Between Substance Use Disorders and Mental Illness. Retrieved from on 2022, April 27
  2. NIDA. 2021, April 13. What are the treatments for comorbid substance use disorder and mental health conditions?. Retrieved from on 2022, April 27
  3. NIDA. 2021, April 13. Why is there comorbidity between substance use disorders and mental illnesses?. Retrieved from on 2022, April 27
  4. NIDA. 2021, April 13. What are the treatments for comorbid substance use disorder and mental health conditions?. Retrieved from on 2022, April 27