In 1991 the World Health Organization commissioned the original Global Burden of Disease (GBD) study. The study produced 1990 estimates for 107 diseases and injuries and ten risk factors for eight world regions. The study is the source of the often-cited reference to depression as the leading cause of disability in the world. Estimates from the GBD study are used by governments, policy makers, and funding bodies to guide decisions about policy and service development.

A new GBD study is under way to produce 1990 and 2005 estimates of the burden of 175 diseases and injuries and more than 45 risk factors in 21 world regions. In the original study, estimates were based on the disability-adjusted life year (DALY), a time-based estimate that combines years of life lost because of premature mortality and years of life lost as the result of time lived in less than ideal health. In recent years there has been much debate about the methodology used for disability weight estimation, the discounting of future health, and the use of age weighting in the DALY calculations. For the new GBD study, disability weights will be extensively revised on the basis of current empirical work.

Approximately 45 expert groups have been established to cover specific diseases, injuries, and risk factors across five clusters of diseases and injuries: cancer and cardiovascular and chronic respiratory diseases; child and maternal health; injuries and mental health; communicable diseases; and other noncommunicable diseases. The study, which began in 2007, is led by a consortium of Harvard University, the Institute for Health Metrics and Evaluation at the University of Washington, Johns Hopkins University, the University of Queensland, Australia, and the World Health Organization. The three-year project will culminate in the publication of estimates in 2010.

The Mental Disorders and Illicit Drug Expert Group is led by researchers at two centers in Australia: the Queensland Centre for Mental Health Research at the University of Queensland and the National Drug and Alcohol Research Centre at the University of New South Wales. The new study will provide estimates for a greater number of disorders. However, some common conditions, such as personality disorder and benzodiazepine dependence, are likely to be excluded because of a lack of data.

The original GBD study covered unipolar depression, bipolar disorder, panic disorder, obsessive-compulsive disorder, posttraumatic stress disorder, and illicit drug use. The new study will include these disorders plus eating disorders (anorexia and bulimia), dysthymia, generalized anxiety disorder, agoraphobia, social phobia, separation anxiety disorder, pervasive developmental disorders (autism and Asperger's disorder), attention-deficit disorder, and conduct disorder. In the original GBD study, cannabis dependence was not considered, and a limited definition that focused on heroin dependence formed the basis of illicit drug use estimates. The new study will include estimates of burden attributable to heroin and other opiates, cocaine, amphetamines, and cannabis. Estimates for alcohol abuse and dependence will be revised.

The Mental Disorders and Illicit Drug Expert Group is seeking input from individuals and research groups able to provide data on incidence, duration, prevalence, remission, or mortality of mental disorders and illicit drug dependence and to contribute to the debate on burden estimates for these disorders. The group's work is described on its Web site at www.gbd.unsw.edu.au. Feedback can be sent to the group at gbd@unsw.edu.au.