bipolar affective disorder

Last edited 07/2020 and last reviewed 07/2021

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-V) distinguishes between bipolar I and bipolar II disorder - includes the category “bipolar and related disorders,” which encompasses bipolar II, bipolar I, and cyclothymic disorders

  • atypical bipolar-like phenomena that do not fit the canonical subtypes are included in the “other specified and bipolar related disorder” category.

  • 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
      • psychotic symptoms such as delusions and hallucinations occur in up to 75% of manic episodes, and episodes of any severity may compromise psychosocial functioning to the point that hospitalization is required (4)
  • Bipolar II disorder
    • lifetime prevalence around 0.4% (2,3)
    • do not experience mania but have periods of hypomania, depression or mixed states
      • hypomania is characterised by milder elevation of mood and overactivity (lasting at least 4 days) without psychotic features or significant functional impairment
      • presence of at least one hypomanic episode in a life trajectory is considered to be consistent with the diagnosis of bipolar II disorder (4)
  • Cyclothymic disorder
    • characterized by recurring depressive and hypomanic states, lasting for at least 2 years, that do not meet the diagnostic threshold for a major affective episode (4)

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) - a review though suggested that onset of bipolar disorder typically occurs at around the age of 20 years (4)

  • 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 (2)
  • bipolar disorder in children under 12 years is very rare (2)


  • first episode of bipolar disorder is usually depressive, and for most persons with either bipolar I or bipolar II disorder, depressive episodes last considerably longer than manic or hypomanic episodes throughout the course of illness - in some cases bipolar disorder may be misclassified as major depressive disorder (4)
  • bipolar disorder is not diagnosed until 10 years after the onset of symptoms - in up to a third of cases of bipolar disorder
  • approximately 6 to 7% of persons with bipolar disorder commit suicide - suicide rates among persons with bipolar disorder are 20 to 30 times as high as the rates in the general population
  • chronic medical conditions such as metabolic syndrome (affecting 37% of patients with bipolar disorder),migraine (35% of patients with bipolar disorder),obesity (21% of patients with bipolar disorder), and type 2 diabetes mellitus (14%of patients with bipolar disorder) - occur at increased prevalence in patients with bipolar disorder than the general population


  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
  4. Carvhalo AF et al. Bipolar Disorder. NEJM 2020;383:58-66.