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Get The Facts

What Is a mental illness?

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Mental Health

What Is a mental illness?

Mental illness is a term that refers to a group of disorders that impact on a person's thoughts, behaviour and emotions, causing significant distress and reduced abilities to cope with everyday life.

Examples, of mental illnesses include depression, anxiety disorders, schizophrenia and personality disorders. A mental illness can vary from mild and temporary, to severe and prolonged.

Generally a mental health issue can be overcome by internal coping tools and support from others. A mental illness is more severe and requires professional treatment and support. It will often cause difficulties in:

  • Coping with stress, anger and other emotions
  • performing daily activities e.g. cooking, cleaning, personal hygiene
  • Undertaking family responsibilities
  • Finding and retaining employment
  • Having healthy relationships with others
  • Structuring the day. 


What causes mental Illness?

The causes are thought to be biological or genetic factors that create vulnerability, or predispostion, to mental illness. Events in life such as chronic stress, major changes or drug use may trigger a mental illness when a person is predisposed to mental illness. 


Classes of mental illness

There are several main classes of mental illness. 


Mood disorders are those that change how you feel, such as persistent sadness or feelings of euphoria. They include major depression and bipolar disorder.


Anxiety disorders involve anxiety that is out of proportion to what is normally considered anxiety-provoking. Examples include panic disorder, obsessive-compulsive disorder, specific phobias and generalized anxiety disorder.


Substance-related disorders include problems associated with the misuse of alcohol, nicotine, caffeine and illicit drugs.


Psychotic disorders impair our sense of reality. The most notable example of is schizophrenia, although other classes of disorders can be associated with psychosis at times.


Cognitive disorders influence your ability to think and reason. They include delirium, dementia and memory problems. Perhaps the most well-known of these disorders is Alzheimer's disease.


Developmental disorders cover a wide range of problems that usually first begin to make themselves known in infancy, childhood or adolescence. They include Autism, attention-deficit/hyperactivity disorder and learning disabilities. 


Personality disorders are an enduring pattern of inner experience and behaviour that is dysfunctional and leads to distress or impairment. Examples include borderline personality disorder and antisocial personality disorder.


Other disorders is a group including disorders of impulse control, sleep, sexual functioning and eating. Also included are dissociative disorders, in which a person's sense of self is disrupted, and somatoform disorders, in which there are physical symptoms in the absence of a clear physical cause, such as hypochondriasis. 


Mental illness & brain injury (dual diagnosis)

Mental illness can occur at the same time as a brain injury and is known as dual diagnosis or co-morbidity. A mental illness may have been present prior to a brain injury or a person may have a history of mental illness prior to acquiring a brain injury.


According to a recent publication released by the Australian Institute of Health and Welfare, 42% of people with a brain injury surveyed had a psychiatric disability.1 Research has indicated that traumatic brain injury is linked to the development of mental illness.2


Separating the symptoms of a mental illness and an acquired brain injury is a difficult task. The symptoms of ABI and a mental illness can be extremely similar, causing problems for diagnoses and therefore access to appropriate treatment.

A mental illness may be developing after brain injury if there is:

  • A gradual decline in ability to perform everyday tasks
  • Decline in ability to cope with every day stressors
  • Increased behavioural issues e.g. anger, frustration, agitation
  • Exaggeration of the effects of the acquired brain injury.


If a mental illness is suspected it is important to seek advice from a qualified mental health professional or local GP. 

References and further information

For more information, contact the Mental Health Association in your state, via


Mental Illness Fellowship of Victoria (2008). Frequently asked questions about mental illness. Accessed 5 August 2009, from

1 Australian Institute of Health and Welfare (2007). Bulletin 55: Disability In Australia: acquired brain injury. Accessed 5 August 2009, from

2 Can Traumatic Brain Injury Cause Psychiatric Disorders?


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