Substance Misuse and Mental Health Disorders: Is Addiction a Mental Illness?

Substance use disorders and mental health disorders often occur simultaneously. In fact, there are synonymous terms—co-occurring disorder and dual diagnosis—to describe this very condition, which is relatively common.

According to insights from the 2021 National Survey on Drug Use and Health (NSDUH), 46.3 million people aged 12 and older in the U.S. (i.e., 16.5% of the population) had a substance use disorder (SUD) in the past year. The same study revealed that nearly 1 in 4 adults aged 18 and older had a mental illness in the same timeframe. The demographic group with the highest incidence of both an SUD and a mental health disorder was young adults, as 13.5% of those aged 18 to 25 received this dual diagnosis.¹

Is Addiction a Mental Illness?

Yes, addiction—clinically known as substance use disorder (SUD)—is considered a behavioral health disorder. SUD is characterized as compulsive substance use despite it causing clinically significant impairment in one’s life.²

Despite the heavy stigmatization of drug and alcohol use, recovery from addiction is not a matter of willpower. It is a relapsing condition not unlike other chronic illnesses such as diabetes or heart disease. However, it is treatable and many people are able to achieve long-term recovery through evidence-based care.³

What is Substance Use Disorder?

A Substance Use Disorder (SUD) is a medical condition defined by the inability to control the use of a particular substance (or substances) despite harmful consequences. When an SUD is severe, you’ll often hear the term used interchangeably with “addiction.”⁴

What is a Mental Health Disorder?

Mental disorders comprise several diagnoses including: generalized anxiety disorder, panic disorder, post-traumatic stress disorder (PTSD), depression, bipolar disorder, attention-deficit hyperactivity disorder (ADHD), psychotic illness, borderline personality disorder, antisocial personality disorder, schizophrenia, and more.⁵

When addiction and another mental health disorder occurs in one patient—regardless of whether one started before the other—this is known as a “dual diagnosis” or “co-occurring disorder” to refer to these co-mingling of conditions.⁶

How Addiction Changes the Brain

Drugs increase activity of dopamine—a brain chemical associated with motivation and reward—in the brain. Large amounts of dopamine “teach” the brain to crave repeating certain behaviors. In this case, it makes someone want to repeat drug use.⁷

The reward circuits in the brain also begin to link certain cues (e.g., environments, people, smells) with drug use. When in these situations, people with an addiction often experience uncontrollable cravings. This can persist for many years (even decades) after someone quits drugs.⁷

Chronic drug use can impact the following areas of the brain:⁷

• The basal ganglia, which is known as the main motivation and reward circuit of the brain. After repeated drug use, the basal ganglia adapts to the presence of the drug, diminishing the ability to feel pleasure without the drug.
• The extended amygdala, which is involved in stress, anxiety, irritability, and other feelings. This part of the brain becomes highly sensitive after prolonged drug use, causing them to experience withdrawal when their high fades.
• The prefrontal cortex, which is the decision-making center of the brain, used to plan, solve problems, and resist impulses. As chronic drug use shifts balance away from the prefrontal cortex toward the basal ganglia and extended amygdala, it becomes increasingly difficult to exercise impulse control.

Risk Factors for Mental Health and Substance Use Disorders

Although a mental health disorder doesn’t always directly cause an SUD (and vice versa), it’s possible that one condition can lead to the other. In fact, according to the National Alliance on Mental Illness (NAMI), those with a mental illness are more susceptible to an addiction, as substance misuse is twice as prevalent among adults with mental illness.⁶

NAMI also suggests that substance use can worsen mental health issues, and ongoing substance use can increase the risk of developing mental illness. In addition, the likelihood of substance use increases with the severity of mental illness. NAMI data also reveals that those with a mental illness consume a relatively high proportion of substances. Specifically, they consume more than 50% of opioid prescriptions, 44% of cocaine, and 38% of all alcohol.⁶

It’s difficult to tell which disorder led to the other—and dual diagnosis doesn’t mean that this causality even exists. However, the National Institute on Drug Abuse asserts that there are several common risk factors that can contribute to comorbidity between these two disorders:⁵

1. Genetic vulnerabilities. Roughly 40% to 60% of a person’s vulnerability to SUDs can be attributed to genetics. Sometimes genes can act directly, such as when a protein impacts how someone responds to a drug or how long the drug stays in their body. Or, genes can act indirectly by influencing risk-taking behavior, stress response, etc. Thus, research suggests that genetics can contribute to the risk of both SUDs and mental health disorders.
2. Brain region involvement.  The brain circuits that control reward, decision making, impulse control, and emotions can be affected by substances and disrupted by substance use disorders, depression, schizophrenia, and other psychiatric disorders.
3. Environmental influences. Environmental factors, such as chronic stress, trauma, and adverse childhood experiences, are linked to a higher risk for both SUDs and mental illness.
4. Stress. Stress is a well-known risk factor for various mental disorders, and it can be seen as a common neurobiological link between the disease processes of both substance use disorders and mental disorders.
5. Trauma and adverse childhood experiences. Those who have been emotionally or physically traumatized have a considerably higher risk of SUDs. As such, mental disorders such as PTSD are linked to SUDs, as substances may be used as an attempt to reduce anxiety and avoid PTSD consequences.
6. Epigenetic influences. Genetic and environmental factors can interact on the molecular level. To put it simply, environmental factors, such as chronic stress, trauma, and drug exposure, can cause long-lasting changes in gene expression that can affect the functioning of neural circuits. Ultimately, these changes can impact behavior.

Treatment for Co-Occurring Disorders

Experts used to think SUDs and mental health disorders should be treated separately. However, new findings indicate that it’s important to treat both conditions simultaneously in order to achieve long-term recovery. Typically this treatment involves cognitive behavioral therapy strategies to boost coping and interpersonal skills while also using approaches to support functional recovery and motivation.⁵

Behavioral therapies used alone or alongside medications are the cornerstones for co-occurring disorder treatment. Strategies that have shown significant promise include:⁵

• Cognitive Behavioral Therapy (CBT).
• Dialectical Behavior Therapy (DBT).
• Contingency Management (CM) or Motivational Incentives (MI).
• Exposure Therapy.
• Integrated Group Therapy (IGT).
• Assertive Community Treatment (ACT).
• Therapeutic Communities (TCs).
• Seeking Safety (SS).

If you or someone you love has a substance use disorder or co-occurring disorder, American Addiction Centers can help. With inpatient treatment facilities and outpatient programs scattered across the country, AAC offers evidenced-based treatment for co-occurring conditions and SUDs. Reach out to one of our confidential admissions navigators at or via text to learn more about which treatment options are right for you. Take your first steps toward recovery today.