A new study says more than 164 million people in Europe suffer from mental ailments, and only one-third are being treated.

The three-year survey, released Monday, covered 30 European countries with a population of more than a half-billion people. It concluded that 38 percent of the population was suffering from mental disorders ranging from anxiety to schizophrenia.

The study found that the most disabling conditions are depression, dementia, alcohol dependence and stroke. According to the survey, women are more likely than men to suffer from depression.

The study also noted that while brain illnesses were on the rise, large drug companies are investing less in research on how the brain works.

The study was led by Hans Ulrich Wittchen of Germany's Dresden University and published by the European College of Neuropsychopharmacology.