background Rapid cycling is a form of bipolar disorder that is characterised by frequent episodes and poor response to pharmacotherapy. It is uncertain whether rapid cycling is a distinct subtype of bipolar disorder, possibly with a different pathophysiological background.

aim To determine whether rapid cycling and can be distinguished from non-rapid cycling bipolar disorder on the grounds of patient characteristics, clinical characteristics other than episode frequency, and treatment response.

method We reviewed and meta-analysed the existing literature. In addition, we conducted a prospective study of 539 bipolar patients, adopting both a dichotomous and a dimensional approach to episode frequency.

results Rapid cycling was associated with various demographic, biographic, and psychiatric factors. These gradually became more prevalent with increasing episode frequency, but there was no evidence of a sharp division between rapid and non-rapid cycling. Depressive symptoms predominated in bipolar patients; manic symptoms increased as a function of episode frequency. Lithium remains the treatment of choice in the case of rapid cycling: there is no evidence that other mood stabilisers are more effective.

conclusion Rapid cycling is not a distinct subtype of bipolar disorder, but should be regarded as one of the two extremities on a continuum of episode frequencies.