Bipolar disorder is a mood disorder characterised by alternating periods of euthymia, hypomania, mania, mild depression, and/or major depression. Individuals unaffected by a mood disorder tend to have a more consistent euthymic mood state. People with bipolar disorder can experience a high and low mood simultaneously, which is called a mixed episode. Bipolar disorder can be associated with psychotic features such as hallucinations, which are often mood congruent. While bipolar disorder is predominantly viewed as a mood disorder, its symptoms are more far-reaching, including changes in sleep, speech, cognitions, and physical functioning. Bipolar disorder occurs in around 1% to 3% of the population. It has a high genetic loading, with a 10% chance of inheriting it if one parent has the condition and 40% chance if both parents have it. Bipolar disorder is considered one of the most severe mental illnesses as it is lifelong, tends to be chronically relapsing for some, and is associated with a large amount of morbidity combined with a large number of episodes of self-harm, suicide attempts, and suicide completions. The most common comorbidities for bipolar disorder are anxiety and substance use. The World Health Organisation's (WHO) “burden of disease” report in 1996 (Murray & Lopez) ranked bipolar disorder as sixth in terms of overall disability among those aged 15–44 years. People with bipolar disorder die much earlier than the general population, often due to preventable health-related disorders such as smoking-related health issues, cardiovascular disease, and diabetes. Bipolar disorder is associated with a 20% to 50% risk of a suicide attempt (Jamieson, 2000).
The Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association, 2013) recognises that bipolar disorder occurs on a spectrum of disorders including cyclothymic disorder, bipolar II disorder, bipolar I disorder, and other specified bipolar disorder. The DSM-5 criteria for depression and mild depression are discussed in Chapter 10. The elevated moods in bipolar disorder are hypothymia and mania as distinguished by severity, with mania the more severe elevated mood. Hypomania is an elevated state lasting up until four days whereas mania lasts more than 1 week and is associated with impaired functioning, hospitalisation, and psychotic features.