The Relationship between Mental Health and Comorbid Substance Misuse

The term comorbidity refers to two health conditions that co-occur in an individual. The high probability of mental illness and comorbid substance abuse occurring in individuals makes it a subject worth investigating.

Interestingly, research indicates that comorbidity conditions cause each other and reinforce each other negatively, creating higher risk factors and a greater need for treatment.

A Common Problem

This is genuinely a stimulating and complex subject as it mimics the age-old chicken and egg dilemma. Which came first?

Establishing a clear connection and causality between both conditions is troublesome due to the acute or chronic effects of substance misuse, which can mimic the symptoms of several mental health illnesses. Mental health disorders can also negatively impact substance use by kickstarting substance abuse, increasing drug use, or creating dangerous patterns. [1]

Furthermore, compelling evidence and a high number of substance misuse sufferers also diagnosed with mental illness (and vice versa) support a comorbidity relationship between the two conditions.

However, the comorbid nature of the two disorders can fluctuate depending on the disorder. For example, depression, psychosis, post-traumatic stress disorder combined with the substance alcohol, cannabis, opioids, or stimulants can all have a varied impact.

Just because there is a correlation (a connection between two things) does not mean there is cause and effect. Yes, substance use disorders often do occur together with other mental illnesses, but it is impossible to say which one caused the other. [2]

Shared Risk Factors

Researchers have found several risk factors that increase the chances of an individual suffering from mental illness and comorbid substance misuse.

Your genes may affect how you respond to a drug, creating be a significant risk factor for developing substance abuse and mental illness disorders.

An example of this would be an individual who frequently used marijuana during childhood and has a specific gene that increases the risk that one will exasperate or bring on the other.

Risks factors also include our surroundings and environmental factors such as stress and trauma, influencing mental illnesses or substance use disorders. In addition, research indicates that these can cause genetic changes, which can become hereditary.

Mental illness can also be a risk factor for drug use and substance use disorders, as studies show those suffering from some mental illnesses may self-medicate with drugs or alcohol.

During the development of mental illness, the brain goes through changes that may increase any reward effects when ingesting drugs.

This means that drugs can make mental illness worse and prompt the individual to compulsively abuse a substance, resulting in changes that make developing a mental illness more likely.

Furthermore, trauma and difficult childhood experiences can be risk factors for the co-occurrence of substance misuse disorders and mental health disorders.

The chances of these disorders occurring together in physically or emotionally traumatized people are high, with an additional increased risk of inferior or unsuccessful treatment outcomes. For example, people living with PTSD may use drugs to reduce their anxiety and block any trauma. [3]

Lastly, but perhaps most predominantly, is the negative impact of stress on the comorbidity relationship. Stress provides a probably neurological link between the disorder processes of substance use disorders and mental illnesses. Relapse is also much more likely to drug use even after recovery when exposed to stressors. [4]

Impact of Specific Mental Illnesses

The comorbid relationship between mental health and substance use disorders differs based on the combination of the two disorders and how they interact. Therefore, it is essential to consider the specific conditions when establishing a relationship.

For example, there is a high vulnerability to develop a substance use disorder in those suffering major depression. These substance users are also at a higher risk of developing major depression.

Psychosis and substance use also impacts this relationship as psychotic disorders often trigger a predisposed individual who uses drugs.

Schizophrenia and bipolar disorder are the most prevalent forms of psychosis in substance users, potentially because drugs can cause acute psychotic episodes in users with an underlying psychotic disorder.

There are complicated connections between anxiety and substance use disorders as users may attempt to reduce their feelings of anxiety with self-medication in the form of drugs. However, anxiety can also be the consequence of inebriation or withdrawal.

Antisocial and borderline personality disorders are the most diagnosed in illicit substance users. Individuals with personality disorders will experience more challenging substance use disorders than those without, and often find it harder to remain in a treatment plan. They are also more likely to engage in risky behaviours such as unprotected intercourse and unhygienic injection practices.

Lastly, there is also interest and evidence suggesting a comorbidity pattern in other mental health conditions such as deficit hyperactivity disorder (ADHD) and eating disorders.[5]

Clinical Assessment

The difficulty in separating the overlapping symptoms of comorbid substance use disorders and mental illness makes forming a diagnosis and treatment plan complicated.

Patients suffering from both conditions regularly display signs that are more acute, relentless, and resilient to treatment in contrast to patients suffering only one of these disorders.

A complete diagnosis and intervention are required to reduce the chance of an incorrect or missed diagnosis. Intervention should also consist of a cohesive approach that identifies and evaluates each disorder in conjunction and allows a treatment plan to be formulated appropriately.

In addition, improved treatments and reduced social stigma can be achieved from a complete understanding of these disorders’ shared genetic, neural, and environmental basis.

Diagnosing and treating comorbidity patients accurately is yet again complicated by the similarities between drug-related symptoms, such as withdrawal, and potentially comorbid mental disorders.

Therefore, patient screening for substance use disorders during treatment for psychiatric illnesses and vice versa.

Consequently, when substance misuse disorder patients are beginning treatment, it may be essential to observe the patients following a period of abstinence. It then becomes easier to spot a potential distinction between the effects of mental health disorders and the symptoms of comorbid substance intoxication and vice versa.

This allows for more accurate diagnosis and better-targeted treatment. [6]


Unfortunately, patients with comorbid disorders often find it challenging to stick with their treatment, and a higher dropout rate occurs compared to those who do not have a mental illness. This ultimately has a negative effect on their recovery.

A combined treatment plan has proven the best chance of recovery rather than receiving treatment for each disorder alone.

Treatment for comorbidity disorders often involves using cognitive behavioural therapy (CBT), which boosts interpersonal and coping skills. This integrated approach provides support, motivation, and functional recovery.

Other behavioural therapies include dialectical behaviour therapy (DBT), assertive community treatment (ACT), therapeutic communities (TCs) and exposure therapy, although this list is not exhaustive.

Behavioural treatment is an essential foundation for achieving successful long-term recovery for substance abuse disorders and mental illness disorders.

However, this treatment can have the most success when combined with effective medications for treating opioid, alcohol, and nicotine use disorders. In addition, these medications alleviate the symptoms of many other disorders and reduce the need for illegal substance misuse.

This integrated treatment is often the result of a collaboration between healthcare providers and organizations that provide supportive services regarding homelessness, physical health, vocational skills, and legal problems. [7]


Diagnosing and treating a mental illness and comorbid substance abuse disorder will always be challenging due to the symptoms that mimic each other or cause the onset of one another. Despite this difficulty, there is plenty of research to say that an impacting relationship between mental illness and comorbid substance abuse exists. Although it may not be clear currently which disorder causes the other, the optimistic take home is that combined treatment is available to anyone who needs help overcoming either condition.