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bipolar disorder

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Bipolar affective disorder is a condition where there are periodic swings of mood periods of months or years between manic episodes and depressed episodes (1).

Bipolar disorder is a potentially lifelong and disabling condition characterised by episodes of mania (abnormally elevated mood or irritability and related symptoms with severe functional impairment or psychotic symptoms for 7 days or more) or hypomania (abnormally elevated mood or irritability and related symptoms with decreased or increased function for 4 days or more) and episodes of depressed mood. It is often comorbid with other disorders such as anxiety disorders, substance misuse, personality disorders and attention deficit hyperactivity disorder (ADHD) (2).

The American Psychiatric Association's Diagnostic and Statistical Manual (DSM-IV) distinguishes between bipolar I and bipolar II disorder:

  • Bipolar I disorder:
    • lifetime prevalence of around 1% (2,3)
    • characterised by episodes of depression, mania or mixed states separated by periods of normal mood
      • features of mania include elevated, expansive, euphoric mood, irritability and hyperactivity, decreased need for sleep, disorganised behaviour, delusions, hallucinations and significant (often severe) functional impairment
  • Bipolar II disorder
    • lifetime prevalence around 0.4% (2,3)
    • do not experience mania but have periods of hypomania, depression or mixed states
      • hypomania, as defined by DSM-IV, is characterised by milder elevation of mood and overactivity (lasting at least 4 days) without psychotic features or significant functional impairment

In both bipolar I and bipolar II disorder, depression tends to predominate over elevated mood in the overall course of the illness

Note also that at some stage in their illness, around 14-53% of patients are reported to develop 'rapid cycling' - defined as four or more manic, hypomanic, depressive or mixed episodes occurring within 12 months (1)

The peak age of onset is 15-19 years, and there is often a substantial delay between onset and first contact with mental health services (2)

  • lifetime prevalence of bipolar I disorder (mania and depression) is estimated at 1% of the adult population, and bipolar II disorder (hypomania and depression) affects approximately 0.4% of adults
  • bipolar disorder in children under 12 years is very rare.


  1. Drug and Therapeutics Bulletin 2005; 43(4):28-31.
  2. NICE (September 2014). Bipolar disorder: the assessment and management of bipolar disorder in adults, children and young people in primary and secondary care
  3. NICE (April 2018). Bipolar disorder: assessment and management


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