Nearly 40 percent of Europeans suffer mental illness

With only about a third of cases receiving the therapy or medication needed, mental illnesses cause a huge economic and social burden -- measured in the hundreds of billions of euros -- as sufferers become too unwell to work and personal relationships break down.

"Mental disorders have become Europe's largest health challenge of the 21st century," the study's authors said.

At the same time, some big drug companies are backing away from investment in research on how the brain works and affects behavior, putting the onus on governments and health charities to stump up funding for neuroscience.

"The immense treatment gap ... for mental disorders has to be closed," said Hans Ulrich Wittchen, director of the institute of clinical psychology and psychotherapy at Germany's Dresden University and the lead investigator on the European study.

"Those few receiving treatment do so with considerable delays of an average of several years and rarely with the appropriate, state-of-the-art therapies."