Dual Diagnosis; The Link Between SUD and Mental Health Treatment

By: Lakeview Health Staff
Published: July 2, 2012

Dual diagnosis is a term that refers to the comorbidity, or co-occurring condition, of both substance use disorder (SUD) and mental illness within the same person at the same time. A dual diagnosis is considered more difficult to treat than a mental illness or drug addiction alone. There is controversy in the field of psychiatry about what causes a dual diagnosis and how it can best be treated. This guide provides an introduction to some of the key issues regarding dual diagnosis. 

Overview of Dual Diagnosis 

It is common for substance abuse to develop simultaneously with certain types of mental illness such as schizophrenia, depression, bipolar disorder and anxiety. The 2021 National Survey on Drug Use and Health found that about 9.2 million adults in the US have a dual diagnosis/co-occurring disorder. In fact, more than 50 percent of those diagnosed with a SUD are also diagnosed with a mental health disorder and it is estimated that nearly 30 percent of individuals with a mental illness also have a substance abuse problem.  Among individuals with severe mental disorders like bipolar disorder, the number of people addicted to drugs can rise as high as 60 percent. Understanding of dual diagnosis is a continuing field of research and experts still do not agree on what causes drug addiction to develop alongside mental illness. 

  • Results from the 2021 National Survey on Drug Use and Health: This resource has statistics and general information indicators of substance use and mental health among people aged 12 years old or older in the United States.
  • Substance Use and Co-Occurring Mental Disorders: This directs you to the National Institute of Mental Health’s page on SUD and other co-occurring mental health disorders. Here you can find information on statistics, what these co-occurring disorders are and common treatments for this diagnosis with the resources to explore specific topics on a deeper level.
  • Addiction: This website explains substance use disorder’s causes, signs and symptoms, treatment and prevention. The site also contains this information for most mental health disorders, making it a great resource for understanding all co-occurring mental illnesses.

Theories on Dual Diagnosis Causes 

There are several theories on what causes a dual diagnosis condition to develop. Multiple environmental risk factors such as poverty, trauma and adverse childhood experiences (ACEs) can work together to make an individual more likely to have co-occurring mental illness and drug addiction.  Supersensitivity theory states that some individuals are biologically and developmentally vulnerable to developing psychiatric disorders and that even small amounts of a substance can lead to drug addiction. 

Although no single cause has been identified, there are various theories on how mental illnesses may interact and contribute to the development of a dual diagnosis. Some of these theories include: 

  • Common factor theory: This theory considers that some risk factors (such as antisocial personality disorder and genetic predisposition) are shared in both disorders, making the person more vulnerable to developing them both. 
  • Secondary substance use disorder model: This theory suggests that the individual first develops their co-occurring mental illness (such as schizophrenia or bipolar disorder) and this makes them more vulnerable to developing a SUD. For example, people with a mood disorder may feel sad or experience dysphoria more often or more intensely than the average person. Attempts to alleviate this emotional pain or dysphoria by self-medicating with substances can lead to the development of a SUD. 
  • Secondary psychiatric disorder model: This theory is opposite to the above theory. It states that a SUD may make someone more vulnerable to developing a mental illness than if they had never misused any substances. The evidence seems to discredit this theory, with some substances, like alcohol, masking symptoms of depression rather than causing them. Those diagnosed with a SUD tend to experience symptoms of a co-occurring mental disorder at a younger age and are more likely to have close family members with the same mental health diagnosis. Rather than the substance misuse causing the development of the dual diagnosis, it is more likely that common risk factors or the increased stressor of substance misuse can explain this. 
  • Bidirectional model: This theory suggests that neither the SUD nor co-occurring disorder “caused” the other to develop. Both disorders exacerbate the symptoms of each other and increase the person’s vulnerability to experience them at the same time. It is a theory that supports the very effective integrated treatment models, treating both disorders together. 

The debate of which disorder came first is very much a chicken or egg question. It seems to provide the hope that we can prevent a dual diagnosis rather than cure it, but it is incredibly complex and probably will not be answered in the near future. There are incredible resources on the topic, and many give great insight into how to understand a dual diagnosis. 

  • Causes of Addiction: This easy-to-digest article in Psychology Today explores the current scientific theories and facts about addiction and what predisposes a person to develop substance use disorder.  
  • Dual diagnosis: A review of etiological theories: This scientific paper is one of the most referenced sources on the causes of dual diagnosis, despite being a bit older.  It looks at all the above theories and models in more detail. 
  • Substance Use and Co-occurring Mental Disorders: Which came first: SUD or the co-occurring disorder? This page explains the complexities of how one disorder can influence the other.  

Dual Diagnosis Treatment Approaches 

Despite disagreements about how dual diagnosis conditions develop, there is a consensus that integrated treatment models are more effective with this population. Integrated treatment begins with a detoxification process in which an individual ceases use of addictive substances. It is generally believed that focusing on the mental disorder first, rather than the addiction, is ineffective. After detoxification, treatment can include a mixture of individual psychotherapy, group counseling, peer support groups and psychiatric medication. Medications used for dual diagnosis cases vary depending on the nature and severity of an individual’s mental disorder. 

Treating a person who has been diagnosed with a co-occurring mental health disorder can be a challenge for medical professionals. It has been shown that those diagnosed with a dual diagnosis often face more resistance to treatment.

These individuals can face various obstacles, such as: 

  • Less engagement with their treatment 
  • More socio-economic challenges 
  • Increased stigma 

These factors may interact and exacerbate each other, but there is always hope. Successful treatment and long-term recovery are possible; they may just be an increased challenge. This is important for the individual and their loved ones to know, as healing takes time and compassion. Every person’s journey will be different and integrative treatment models are very effective.