Has increased provision of treatment reduced the prevalence of common mental disorders? Review of the evidence from four countries.

Many people identified as having common mental disorders in community surveys do not receive treatment. Modelling has suggested that closing this "treatment gap" should reduce the population prevalence of those disorders. To evaluate the effects of reducing the treatment gap in industrialized countries, data from 1990 to 2015 were reviewed from four English-speaking countries: Australia, Canada, England and the US. These data show that the prevalence of mood and anxiety disorders and symptoms has not decreased, despite substantial increases in the provision of treatment, particularly antidepressants. Several hypotheses for this lack of improvement were considered. There was no support for the hypothesis that reductions in prevalence due to treatment have been masked by increases in risk factors. However, there was little evidence relevant to the hypothesis that improvements have been masked by increased reporting of symptoms because of greater public awareness of common mental disorders or willingness to disclose. A more strongly supported hypothesis for the lack of improvement is that much of the treatment provided does not meet the minimal standards of clinical practice guidelines and is not targeted optimally to those in greatest need. Lack of attention to prevention of common mental disorders may also be a factor. Reducing the prevalence of common mental disorders remains an unsolved challenge for health systems globally, which may require greater attention to the "quality gap" and "prevention gap". There is also a need for nations to monitor outcomes by using standardized measures of service provision and mental disorders over time.