Co-Occurring Disorders & Substance Abuse

The key to resolving a problem is to identify its causes and correct them. However, sometimes there is another problem, though it may go unnoticed. If it is noticed, it can be unclear if the two problems are related and, if they are, which came first. Nevertheless, both must be addressed.

Consider a bucket that is losing water. If the problem is only seen as the fact that there is less water in the bucket, then adding more water is the obvious solution. If the loss is due to a hole in the bucket, refilling it is only a temporary solution. If the hole isn’t repaired, the problem will continue and may become worse.

So it is when substance use disorder and mental health disorders co-occur. Unless both are treated, they may continue, recur, or worsen.

What Is a Co-Occurring Disorder?

Also known as dual diagnosis or comorbidity, co-occurring disorders usually involve a substance use disorder (SUD)—also known as substance use disorder disorder or addiction—and a mental health issue—such as depression, anxiety, bipolar disorder, post-traumatic stress disorder, or schizophrenia—but it can also refer to any two medical conditions that occur at the same time, related or not.

Examples of non-SUD comorbidities include diabetes with chronic obstructive pulmonary disease (COPD) or depression with hypertension.

Addiction or Mental Illness?

Addiction is a compulsion to continue to use a substance (especially one that changes the brain’s reward system so that stopping use causes the individual to experience withdrawal pain) or engage in a behavior despite adverse consequences.

Mental illnesses—also called mental health issues—are disorders that impact individuals’ “mood, thinking and behavior” that they suffer frequent stress and find it difficult to function.

It might seem to make no difference whether the mental illness or addiction came first. Addiction to drugs or alcohol is a mental illness. The distinction is still important because different classes of mental illnesses often have different treatments. Identifying co-occurring disorders is most important because, like the bucket, both need to be treated.

How Common Are Co-Occurring Disorders?

The number of people with both a substance use disorder and a mental health issue is hard to determine. According to 2014 statistics, more than 20 million U.S. adults admitted to a substance use disorder and almost 8 million to a SUD and a mental illness. The numbers were likely higher and have probably gone up since.

Numbers might be higher in the other direction. The National Institute on Drug Abuse (NIDA) estimates that approximately half of the people who have any mental health disorder in their lifetime will also have a SUD. For a serious mental illness (SMI), the number is 1 in 4.

The rate may be highest for those younger than 18. Though there has been less research, a study of community-based substance use disorder treatment programs found that more than 60% showed signs of another SMI.

Common Co-Occurring Disorders and Addictions

Among the mental health issues most commonly associated with SUDs are:

Some specific SUDs and mental health issues that often occur include cocaine and major depressive disorders and alcohol and panic disorder.

Is Underlying Mental Illness the Root Cause of Addiction?

According to one study, individuals with severe psychotic disorders are at an increased risk of heavy alcohol consumption, recreational drugs, marijuana, and nicotine. Another study from the National Institute on Alcohol Abuse and Alcoholism found that 56% of those with bipolar disorder had a SUD. It also calculated that a mood disorder such as depression increases the odds of SUD by up to 10%.

Based on this evidence, there is a correlation between SUD and mental illness. However, correlation does not necessarily equal causation.

There are at least three possible reasons for the high rate of co-occurring substance use disorder and mental health disorders:

  • Mental illness causes substance use disorder.
  • Substance use disorder causes mental illness.
  • So, do mental illnesses cause substance use disorders? The answer may be yes and no.

Self-Medication for Mental Illness

The National Comorbidity Study found that most of the individuals who reported both a SUD and mental illness at some point in their lives said the mental health issue came first. One reason that mental illness may lead to substance use disorder, if not exactly cause it, maybe the self-medication hypothesis.

Individuals with mental health issues may realize something is wrong, maybe subconsciously. At least some may use alcohol, drugs, or other substances to self-medicate the symptoms of the mental illness. They may not realize why they are doing it, but they are trying to control it, mask it, or just distract themselves from facing it.

It is a fallible solution that may actually make the mental illness worse and add a SUD.

Mental Illness Or Substance-Induced Disorders?

It is well-documented that the use of some drugs increases the incidence of mental illness, including marijuana and hallucinogens such as MDMA (ecstasy) and LSD. It is not clear how much of the increase is the drugs creating the disorder or just revealing a predisposition.

Sometimes, using or abstinence from certain substances can cause effects that superficially resemble the symptoms of a serious mental illness.

These are known as substance-induced mental disorders. Among the substances that can cause these false positives are:

  • Alcohol
  • Caffeine
  • Cocaine
  • Amphetamines
  • Hallucinogens
  • Nicotine
  • Opioids
  • Sedatives


Among the mental disorders the use of these substances can resemble are:

  • Delirium
  • Dementia
  • Memory loss disorder
  • Psychotic disorder
  • Mood disorder
  • Anxiety disorder
  • Sensory disorder
  • Sexual dysfunction
  • Sleep disorders

Addiction professionals can tell whether a real mental illness or a substance-induced mental illness is based on what substance has been used and abused. For every action, there is an equal and opposite reaction.

In addiction treatment, this is sometimes called the teeter-totter principle. Withdrawal from depressants can cause hyperactivity. Withdrawal from stimulants can lead to a lack of energy. And long-term use of almost any substance can lead to psychosis.

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Do Co-Occurring Disorders Have a Common Cause?

Substance use disorder is a mental illness, so both of these co-occurring disorders may have a common cause:

  • Nature. Genetic predisposition.
  • Nurture. Environmental factors such as trauma experienced in early childhood.

Scientists theorize that the developing brain is more fragile, more susceptible to change by outside stimuli, in childhood through a person’s 20s. This is why, aside from morality, alcohol and drug use in adolescents should be discouraged.

Screening for Co-Occurring Disorders

Although it can be helpful to know whether substance use disorder causes mental illness or vice versa, the most important thing for the individual with co-occurring disorders is to know that they are separate disorders that both require treatment.

If self-medication for mental illness is responsible for a great many cases of substance use disorder, better and earlier mental health evaluation and treatment could prevent many SUDs.

The high correlation between mental illness and addiction means that all clients admitted should be screened for the other.


Medical disclaimer:

Sunshine Behavioral Health strives to help people who are facing substance abuse, addiction, mental health disorders, or a combination of these conditions. It does this by providing compassionate care and evidence-based content that addresses health, treatment, and recovery.

Licensed medical professionals review material we publish on our site. The material is not a substitute for qualified medical diagnoses, treatment, or advice. It should not be used to replace the suggestions of your personal physician or other health care professionals.

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