dual diagnosis

Definition: general term referring to comorbidity or the co-occurrence in the same individual of a psychoactive substance use disorder and another psychiatric disorder. Such an individual is sometimes known as a mentally ill chemical abuser (MICA). Less commonly, the term refers to the co-occurrence of two psychiatric disorders not involving psychoactive substance use. The term has also been applied to the co-occurrence of two diagnosable substance use disorders (see multiple drug use). Use of this term carries no implications of the nature of the association between the two conditions or of any etiological relationship between them. Synonym: comorbidity

Examples of a dual diagnosis might include:

  • a mental health problem or disorder leading to or associated with problematic alcohol and/or other drug use
  • a substance use disorder leading to or associated with a mental diagnosis
  • alcohol and/or other drug misuse worsening or altering the course of a person’s mental illness.

Dual diagnosis is an evolving field and we are still learning to understand causal relationships between substance misuse and mental health problems, and how to develop effective strategies for prevention, treatment and recovery.

A mental illness is a disorder that affects the way a person thinks, feels and behaves.

There are many types of mental illness, which will affect each person differently. Some examples of mental illness include:

People take drugs for a variety of reasons. Drug use becomes problematic when this use negatively impacts a person’s life or the life of those around them. This might include:


  • the use of illegal drugs
  • the use of a legal drug without prescription or in excessive amounts
  • using a drug despite any problems caused by the effects of that drug.


Dual diagnosis

People’s experience of dual diagnosis vary. Someone might experience depression or anxiety when using alcohol. Others may find that their cannabis use makes their schizophrenia worse. It depends on the type of mental health problem and its symptoms, the drugs or alcohol used, and how these combine together. It also depends on the treatment or support the person receives. Some types of treatment may work for some people but not others.1


Which comes first—mental illness or problematic drug use?

It can be difficult to determine which occurs first, the mental illness or the problematic drug use. As we’ve discussed, reasons and links between mental health and substance misuse will vary. Other factors like work, relationship difficulties, or other trauma may increase the risk of a person developing a mental illness or experiencing problematic drug use.1


Issues associated with dual diagnosis

Mental health problems and drug use both have a significant impact on people’s lives and the lives of those around them. When they exist together, other issues may develop such as:


  • a person with a mental illness using alcohol or other drugs to help cope with the symptoms of their illness


  • difficulties with diagnosis and establishing whether the issues the person is experiencing are due mainly to the drugs, the mental illness, or a combination of both


  • difficulties engaging a person into treatment and completing the treatment


  • the relapse of one condition may increase the risk of relapse in the other condition


  • there may be a risk of one problem increasing the risk of the other, or an existing disorder becoming more problematic with the other present.


  • interactions between prescribed medication and alcohol or other drugs can result in unwanted side-effects and can increase the risk of overdose. Taking prescribed drugs as directed by the doctor can also cause problems


  • people with a dual diagnosis experience higher rates of homelessness and social isolation, infections and physical health problems, suicidal behaviour, violence, antisocial behaviour and incarceration


  • the stigma of dual diagnosis can impact on a person’s ability or capacity to deal effectively with their condition.


Considerations for dual diagnosis

Experts suggests a range of factors should be taken into account when screening, treating and managing people with dual diagnosis.

Young people with dual diagnosis are particularly at risk of experiencing poor outcomes. Their age means that their stage of physical, neurological, psychological and social development makes young people more vulnerable.

Dual diagnosis presents specific challenges for Aboriginal people, who may experience high rates of substance misuse.

Substance use among older people can have accentuated and profound impacts because of ageing physiology and reduced social interaction.

As well as differences across ages, the type and pattern of drug and alcohol use varies with culture, gender, peer group and social settings.


Family and friends – what you can do

It can be stressful living with or watching someone you care about with mental health problems use alcohol or other drugs.

Learn about drug use and mental health. The more you know about the symptoms and treatment options, the better equipped you will be to help your friend or family member.

Understand that there may be a level of stigma associated with disclosing mental illness or substance misuse. Friends and family experiencing dual diagnosis need time before they discuss these issues with you.

Encourage the person to get help. Urge your friend or family member to seek professional help—don’t wait to see if the person gets better without treatment.

Be understanding. Let your friend or family member know that you’re there if they need someone to listen to them, encourage them and assist with their treatment.

Be patient. Getting better takes time—even when a person is committed to treatment. Be prepared for setbacks and challenges.

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