First off, the government estimates that one in five adult Americans suffered from some sort of diagnosable mental illness in the past year, according to the 2012 Survey of Mental Health by the Substance Abuse and Mental Health Services Administration.
Young people from 18 to 25 had the highest rate, nearly at 30 percent. But about 5 percent of the U.S. population suffered from a serious mental health problem that “resulted in serious functional impairment, which substantially interfered with or limited one or more major life activities.”
Looking across the world, experts say that cross-cultural differences, social and religious stigmas, and income levels often make it difficult to compare mental health diagnoses rates from country to country. However, the World Health Organization (WHO) estimates that the five developed countries with the highest rates of any kind of diagnosed mental health problems (including substance abuse) are Colombia, France, the Ukraine, New Zealand and the United States, according to a 2009 report.