The study, which was lead by the World Health Organisation, was conducted ahead of the World Bank-IMF Spring Meetings in Washington DC this week, where mental health issues are set to be high on the agenda.
WHO warned that common mental disorders, like depression and anxiety, are on the rise worldwide.
Between 1990 and 2013, the number of people suffering from one or both of the conditions increased by nearly 50%, with those that fall victim to conflict or other crises more likely to be affected.
Despite accounting for 30% of the non-fatal disease burden, the WHO said current investment in mental health is seriously lacking. According to a 2014 WHO survey, governments spend between just 1% and 5% of their health budgets on mental health.
Jim Yong Kim, president of the World Bank, said: “Despite hundreds of millions of people around the world living with mental disorders, mental health has remained in the shadows.”
He stressed that this is not just a public health issue, but also a development issue, with the world losing more productivity than it can afford.
Today’s study found that by scaling up treatment for mental health, countries could see significant social and economic benefits.
While the estimated costs of scaling up treatment in 36 low-, middle- and high-income countries amount to $147bn, the study found this would result in a 5% improvement in labour force participation and productivity, valued at $399.
Health improvements would add a further $310bn in returns on the original investment, it found.
Margaret Chan, director general of WHO, said the study confirms that properly treating depression and anxiety makes economic, as well as medical, sense.
“We must now find ways to make sure that access to mental health services become a reality for all men, women and children, wherever they live,” she stated.
Arthur Kleinman, professor of medial anthropology and psychiatry at Harvard University and an expert on global mental health, agreed mental illness needed to be a global humanitarian and development priority, in every country.
“We need to provide treatment, now, to those who need it most, and in the communities where they live. Until we do, mental illness will continue to eclipse the potential of people and economies.”