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Updated: Sep 6, 2023

The Numbers Do Not Lie. Mental illness and addiction often overlap. Nearly 9 million people have a co-occurring disorder, according to the Substance Abuse and Mental Health Services Administration. Yet, only 7 percent of these individuals get treatment for both conditions. And more than 60 percent receive no treatment at all.

Understanding Comorbidity. Comorbidity is when two conditions, such as mental illness and substance abuse, often co-exist. This means that in many people with addictions, there is an underlying mental health issue as well. While neither condition causes the other, they do often exist together. What's more, one disease can exacerbate the symptoms of the other.

It helps to recognize that both are chronic brain diseases to understand better how comorbidity is possible. When someone struggles with an addiction, their brain has been permanently rewired by the substance they abused. This causes the brain to function differently than before. Like diabetes or heart disease, a person with an addiction must manage his condition for the rest of his life. It is not as simple as stopping drug use or alcohol condition. Many times, this is not possible.

The changes in the brain due to substance abuse occur in the same brain areas impacted by depression, anxiety, schizophrenia, and bipolar disorder. Consequently, it should not be surprising that there is a high rate of comorbidity between addiction and other mental illnesses. While scientists have yet to prove a direct link, some mental health issues increase the risk factors for substance abuse. This means that some people with mental illnesses will turn to alcohol or drugs to cope with the pain of their mental health issues.

Why Addiction and Mental Illness Co-Occur. Even though there is a high rate of comorbidity between addiction and mental illness, it does not mean that one caused the other—even if one condition appeared first. According to the National Institute on Drug Abuse, many factors still need to be considered. For instance:

  • Drug abuse can cause people to experience one or more symptoms of another mental illness. For example, there is an increased risk of psychosis in some marijuana users.

  • Mental disorders can lead to drug or alcohol abuse because some people use substances to self-medicate. For instance, tobacco products sometimes lessen the symptoms of schizophrenia and may improve cognition.

Some evidence also indicates that addictions and mental illnesses are caused by underlying brain deficits, genetic influences, and exposure to trauma early in life.​ For instance, 40 to 60 percent of a person's vulnerability to addiction is estimated to be attributed to genetics. Several regions of the human genome have been linked to an increased risk for substance abuse and mental illness.

Another common factor between mental health issues and addiction is the age at which the symptoms appear. During the teen years, people are still developing, maturing, and growing. As a result, significant changes in the brain occur during adolescence. For instance, teenagers are more prone to take risks and act impulsively. While common among teens, these behaviors can influence the risk of addiction and other mental disorders.

People physically or emotionally traumatized are at a much higher risk of substance abuse and possibly addiction. This connection is particularly concerning for veterans returning to the country. One in five military servicemen and women returning from Iraq and Afghanistan have reported symptoms of post-traumatic stress disorder (PTSD) or major depression.

Some studies suggest that half of all veterans diagnosed with PTSD also have a co-occurring substance abuse problem.

Why It Is Difficult to Diagnose Both Conditions. Co-occurring disorders are sometimes difficult to diagnose. One reason is that the symptoms are often complex and can vary in severity. As a result, it is not uncommon for people to receive treatment for one disorder while the other disorder remains untreated. Sometimes this happens because the symptoms are so similar or overlap. In other words, both mental health issues and addiction can have similar biological, psychological, and social components.

Another reason for not diagnosing both conditions might include inadequate training or screening. In any case, the consequences of undiagnosed, untreated, or undertreated co-occurring disorders can lead to a higher likelihood of experiencing homelessness, jail time, medical illnesses, and even suicide.

People with mental health issues who abuse substances like drugs or alcohol are at an increased risk for impulsive or violent acts. They are also more likely to develop an addiction and end up in legal trouble. And achieving lasting sobriety is increasingly difficult for them.

Treatment When Comorbidity Exists. Research suggests that co-occurring conditions need to be treated at the same time. For the best outcome, it helps when people with an addiction and a mental health issue receive integrated treatment. With integrated treatment, doctors and counselors can simultaneously address and treat both disorders. This, in turn, often lowers treatment costs and creates better outcomes for patients.

Early detection and treatment of both conditions can significantly improve the person's recovery and quality of life. However, it is essential to note that people with both an addiction and another mental illness often have symptoms that are more persistent, severe, and resistant to treatment than patients with either disorder alone. For this reason, maintaining sobriety may be very difficult for them.

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