Intellectual disability and mental illness

In South Australia, one in five people lives with a mental illness such as anxiety, depression, bipolar disorder or personality disorder.

This number is significantly higher for people with intellectual disability. Mental illness can remain undiagnosed because communication difficulties often make it harder for the person with intellectual disability to describe their feelings, concerns, experiences and fears.

Someone who lives with intellectual disability and mental illness is often referred to as having ‘dual disability’.

What is intellectual disability?

Intellectual disability is a developmental disorder not a mental illness.

A person with intellectual disability:

  • has an IQ of about 70 or less (most people have an IQ around 100)
  • often needs help with basic skills including communication, self-care, safety and self-direction
  • has demonstrated problems with these skills since they were a child.

People with intellectual disability may find it harder to:

  • understand concepts and ideas
  • work things out and solve problems
  • concentrate
  • remember things.

Types of mental illness

Mental illness is a mind-related disorder that significantly affects how a person feels, thinks and behaves. This may become so overwhelming that the person finds it hard to cope and live their daily life.

Mental illness can last from a few weeks to many years and is not an intellectual disability.


Major depressive disorder (depression) is a mood disorder that affects a person’s ability to carry out their work and daily life. Ten to fifteen percent of people experience depression at some point in their lives.

Depression is the most common mental illness for people with intellectual disability. Its causes are different for each person but are usually a combination of physical, medical and social factors.

Depression is not the same as grief, which is a normal response to loss. Unresolved and long-term grief may increase someone’s risk of depression. People with an intellectual disability may express their grief differently than other people. Their grieving may take longer or a different path.


Anxiety can range from mild uneasiness that won't go away through to a full panic attack. When anxiety interferes with a person's ability to live a normal life, it becomes an anxiety disorder. This is quite common, with fifteen to twenty percent of people living with some form of anxiety disorder.

Some of the more common anxiety disorders include:

  • generalised anxiety disorder
  • obsessive-compulsive disorder (OCD)
  • panic disorder
  • post-traumatic stress disorder (PTSD)
  • phobias.

Some of the symptoms may include:

  • unrealistic or excessive fear of situations or actions
  • constantly worrying about past or future events
  • obsessive or compulsive behaviour and distress in social situations
  • feeling constantly anxious or stressed including a pounding heart, dizziness, headache and nausea.

Anxiety disorders are different for each person and may include a combination of factors that affect people in different ways.

Bipolar disorder

About one percent of people live with bipolar disorder, which used to be called manic depression. It is a condition where a person experiences mood swings between extreme happiness (mania) and deep sadness (depression) over days, weeks or even months.

The causes of bipolar disorder vary for each person but can be a combination of things such as medical factors, life experiences and events. When a person is experiencing extreme cases of mania or depression they may be confused and not know what is real. This is called psychosis.

Common signs of mania include feeling very happy and excited, needing less sleep than usual, talking a lot, rapid repetitive speech, jumping from one topic to another with little connection and being easily distracted.

For some people with intellectual disability, being easily distracted, skipping from activity to activity, talking a lot and seeking attention is everyday behaviour and does not mean they are ill.


Schizophrenia is a serious mental illness that affects the normal functioning of the brain. About one percent of the general population and three percent of people with intellectual disability experience schizophrenia during their lifetime.

A person with schizophrenia experiences confused thinking, delusions and hallucinations. When these symptoms combine, it may be difficult for the person to tell what is real, a condition called psychosis. Psychosis can lead to extreme changes in behaviour.

It is not clear what causes schizophrenia but a combination of several factors, including physical and environmental influences, are likely to contribute. Excessive use of drugs and alcohol may also have an effect.

Dual disability

There are several reasons that people with intellectual disability tend to have mental illness more often than other people in the community. They may have:

  • fewer friends and people to support them
  • more experience of loss, rejection or being separated from people
  • less control over their lives and lower self-esteem
  • homes where they do not feel comfortable or safe
  • experiences of bullying, abuse or neglect
  • trouble learning skills to help manage stress, solve problems or avoid conflict
  • a sensory disability including trouble seeing, hearing or using other senses.

Mental illness in people with intellectual disability can be overlooked because:

  • the person may find it hard to describe their feelings or experiences
  • the signs of illness may not be obvious or there all the time
  • the person may be taking medicines that affect their feelings or behaviour
  • it may be difficult to tell if the behaviour has happened in the past and to recognise patterns of mental illness
  • the symptoms may be similar to some types of disability, for example, autism spectrum disorder.

Dual disability resources

  • The Centre for Disability Health specialises in clinical services for people with disability - phone 8397 8100.
  • Beyond Words are a series of picture books produced by the Royal College of Psychiatrists (UK) to make communicating easier with people who have difficulty using words. Supporting text and guidelines are also provided for carers, supporters and professionals.
  • Beyondblue is an independent, Australian, not-for-profit organisation providing information and help with depression, anxiety and related disorders - phone 1300 22 4636.
  • SANE Australia has education, a helpline and online forum to improve the lives of people living with mental illness, their family and friends - phone 1800 18 7263.
  • Lifeline has free, trained volunteer counsellors available 24 hours a day - phone 131 114.

Getting help

Mental health emergencies

The SA Health Mental Health Triage Service provides advice in emergencies and is the main point of access into mental health services.

This service is available 24 hours a day, seven days a week.

Phone 13 14 65.

Advice and professional guidance

You should seek professional advice if you are caring for someone whose behaviour has significantly changed. Speak to the person's GP, their case manager, a psychiatrist, psychologist or counsellor.

It is useful for you or another carer to go with the person to their first appointment. Family or carers will be able to provide support and describe the changes they have noticed.

Keeping records will show how often the illness occurs and when. Any change from usual behaviours may be important and help identify if someone is experiencing mental illness.

The professional will consider many things as part of their assessment including:

  • the person’s home, social circle, school and work
  • the person’s family history of mental illness
  • how the person communicates.


Treatment options can be considered once a professional diagnosis is made. Treatments must only be delivered by qualified and accredited mental health professionals. They may include:

  • psychological approaches such as cognitive behaviour therapy and/or counselling
  • medication.

Maintaining a normal routine can help reduce stress levels for a person with mental illness. An organised and stable home environment with meaningful activities can help people feel safe and secure and help their treatment.

Related information

Other websites

Black Dog Institute - mood disorder diagnosis, treatment and support information
Healthy Mind - an Easy Read tool to help people with intellectual disability recognise and regulate their thoughts and feelings
Head to Health - Australian online and phone supports, resources and treatment options
Mental Health First Aid Downloads - resources for intellectual disability and mental health problems or crises
Mind Australia - community mental health support
National Association for the Dually Diagnosed - a US site with training and information on mental health and intellectual or developmental disabilities
Psychiatric Assessment Schedules for Adults with Developmental Disabilities - a set of mental health assessments for people with intellectual disability

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Page last updated 1 August 2022

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