Major depressive disorder (MDD) is a significant mental health problem that is estimated to affect more than 8% of the population in the seven major markets (7MM: US, France, Germany, Italy, Spain, UK, and Japan). GlobalData’s new epidemiology report on MDD estimates that the 12-month total prevalent cases will be 52.4 million in 2021 for the 7MM, 38% higher than previously estimated.

The most important factors that influenced this increase in prevalence are changes in disease definition and more recent epidemiology data from community-based studies. GlobalData’s previous estimate for the epidemiology of MDD in 2016 used the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV). In the upcoming epidemiology report, the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5) is used as the disease definition. DSM-5 was published in 2013, but it has taken many years to see the impact of this change on the epidemiology of MDD. The biggest change between DSM-IV and DSM-5 is the removal of the bereavement exclusion from the diagnosis of MDD. In the DSM-IV, if a person is in a period of bereavement, they are excluded from clinical diagnosis. The removal of this exclusion has allowed more people to be diagnosed with MDD.

New epidemiology studies on MDD prevalence in the US, France, Italy, Spain, the UK, and Japan that have been published in recent years also impacted the understanding of its prevalence. GlobalData’s newest forecast showed that the 12-month total prevalent cases increased in the US by 58.7%, in France by 34.7%, in the UK by 31.2%, and in Japan by 18.1%. GlobalData’s analysis showed that MDD prevalence rates are consistently higher than previously thought in these markets, even after controlling for differences in diagnostic criteria. The cause of these increases is unclear, although it could be due to improvements in disease awareness, increased healthcare seeking, and decreased mental illness stigma.

GlobalData epidemiologists expect the prevalence of MDD prevalence to increase after the Covid-19 pandemic as well. Studies in Canada, the UK, and the US have found increases in depressive symptoms in 2020. In a survey conducted by the UK’s Office for National Statistics, depression symptoms were reported by almost one in five adults during June 4–10, 2020, which is twice as high as before the Covid-19 pandemic. However, depressive symptoms are not equivalent to clinical MDD. Thus, more research is necessary to better understand the impact of Covid-19 on MDD epidemiology. MDD may join lung fibrosis, myocarditis, and Alzheimer’s disease as one of the many long-lasting sequelae of the Covid-19 pandemic.