Dr. Kessler serves as Director of the World Mental Health (WMH) Survey Consortium, established by the World Health Organization (WHO) and comprised of researchers from around the world who carried out WMH surveys to facilitate cross-national comparative analysis. This consortium carries out targeted analyses about various issues of interest from an epidemiological perspective, including analyses of prevalence, disorder sub-types, risk factors, and adverse societal consequences. 

This project was created after a number of WMH collaborators expressed great interest in bipolar disorder and also in establishing a workgroup to focus on the epidemiology of bipolar disorder. The project focuses on carrying out analyses on the prevalence and correlates of rapid-cycling bipolar disorder in the National Comorbidity Survey Replication (NCS-R) and the larger World Health Organization (WHO) World Mental Health (WMH) Survey Consortium dataset.

The essential feature of a rapid-cycling Bipolar Disorder is the occurrence of four or more mood episodes during the previous twelve months. These episodes can occur in any combination and order. The episodes must meet both the duration and symptom criteria for a Major Depressive, Manic, Mixed, or Hypomanic Episode and must be demarcated by either a period of full remission or by a switch to an episode of the opposite polarity. Manic, Hypomanic, and Mixed Episodes are counted as being on the same pole (e.g., a Manic Episode immediately followed by a Mixed Episode counts as only one episode in considering the specifier With Rapid Cycling). Except for the fact that they occur more frequently, the episodes that occur in a rapid-cycling pattern are no different from those that occur in a non-rapid-cycling pattern. Mood episodes that count toward defining a rapid-cycling pattern exclude those episodes directly caused by a substance (e.g., cocaine, corticosteroids) or a general medical condition.

Rapid cycling occurs in approximately 10%-20% of individuals with Bipolar Disorder seen in Mood Disorders clinics. Whereas in Bipolar Disorder in general the sex ratio is equal, women comprise 70%-90% of individuals with a rapid-cycling pattern. The mood episodes are not linked to any phase of the menstrual cycle and occur in both pre- and postmenopausal women. Rapid cycling may be associated with hypothyroidism, certain neurological conditions (e.g., multiple sclerosis), Mental Retardation, head injury, or antidepressant treatment. Rapid cycling can occur at any time during the course of Bipolar Disorder and may appear and disappear, particularly if it is associated with antidepressant use. There is some evidence that some individuals with rapid cycling have an acceleration of their cycling rate after exposure to antidepressant medication. The development of rapid cycling is associated with a poorer longer-term prognosis.