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HomeCo-occurring Disorders

Severe Mental Illness Defined
by Duration and Disability

Severe mental illness is often defined by its length of duration and the disability it produces. These illnesses include disorders that produce psychotic symptoms, such as schizophrenia and schizoaffective disorder, and severe forms of other disorders, such as major depression and bipolar disorder.

Illnesses that produce distortions of perception, delusions, hallucinations, and unusual behaviors are sometimes called thought disorders. Because the symptoms reflect a loss of contact with perceived reality, the disorders are also sometimes known as psychotic disorders.

Severe mental illnesses are treatable, and with proper treatment and management of the illness, people with these disorders can experience recovery.

A fact sheet in PDF format detailing symptoms, causes, and treatment for each of these disorders is available.


Schizophrenia is the most common thought disorder. It is not a "split personality" or a "multiple personality."

Symptoms of schizophrenia fall into four categories:

Psychotic symptoms
(also called positive symptoms)

  • Hallucinations
  • False perceptions
  • False beliefs
  • Bizarre behavior
  • Disordered speech
  • Delusions

Negative symptoms

  • Apathy
  • Loss of interest
  • Poor follow-through
  • Loss of pleasure
  • Illogical, limited amount of speech
  • Lack of facial and vocal expressions

Cognitive symptoms

  • Problems with attention, psychomotor speed
  • Slower processing of information, memory, planning and organizing


  • Problems with depression, anxiety, anger, mood shifts
Download a fact sheet about schizophrenia (PDF)

Schizoaffective disorder

Schizoaffective disorder is quite similar to schizophrenia, and is usually long-term.

People with either schizophrenia or schizoaffective disorder can have symptoms of depression, mania, or both types of symptoms. However, people with schizoaffective disorder tend to have more severe depressive or manic symptoms. This means that the symptoms occur more often and last for longer periods of time.


Depressive symptoms

  • Feeling hopeless, sad
  • Loss of interest
  • Significant weight change
  • Trouble sleeping or oversleeping
  • Feeling restless or sluggish
  • Feeling worthless or guilty
  • Difficulty concentrating
  • Irritability
  • Thoughts about death or suicide

Manic symptoms

  • Euphoric or irritable mood
  • Decreased need for sleep
  • Grandiosity (thinking you have abilities or powers you don't have)
  • Spending more money than you have
  • Rapid speech and movements
  • Distractedness
Download a fact sheet about schizoaffective disorder (PDF)

Bipolar disorder

Bipolar disorder causes extreme mood swings ranging from mania or extreme happiness, grandiosity, euphoria or irritability, or decreased need for sleep. Typically a person with bipolar disorder cycles from one extreme to the other while experiencing periods with few or no symptoms in between.

Bipolar disorder is not simply having mood swings. Typically, bipolar disorder involves dramatic shifts not only in mood but in overall outlook, behavior, and energy level.

The cycles of bipolar disorder include depression, mania and what is referred to as a "mixed state."

The manic symptoms of bipolar disorder include:

  • Decreased need for sleep
  • Inflated self-esteem or grandiosity
  • Racing thoughts
  • Distractibility
  • Increase in goal-directed activities
  • More talkative then usual or more pressured speech
  • Excessive involvement in pleasurable activities that often are self-defeating
Download a fact sheet about bipolar disorder (PDF)
Also of interest

Types of disorders
Other mental health disorders found in co-occurring disorders include:

Effective treatment
Co-occurring substance use and mental health disorders need to be treated at the same time.

Peer support and other resources
Peer support groups, advocacy groups, and public policy agencies can help you and your clients learn more about behavioral health.

Frequently asked questions
Find answers to frequently asked questions about co-occurring disorders.

An effective, integrated
treatment program


The Co-occurring Disorders Program is the first comprehensive treatment program for people with non-severe mental health disorders that co-occur with substance use disorders. Learn more

Professional Development

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