One out of every two people in the world will develop a mental health disorder in their lifetime, according to a large-scale study co-led by researchers from Harvard Medical School and the University of Queensland.

The findings are based on structured, face-to-face surveys of more than 150,000 adults across 29 countries of varying wealth from all of the regions of the world. The results are published in The Lancet Psychiatry.

Massive burden of disease

The researchers said the results demonstrate the high prevalence of mental health disorders worldwide, with 50 percent of the population developing at least one disorder by the age of 75.

The findings provide valuable insights into the frequency and timing of mental disorder onset across many different populations, the researchers said.

Ronald Kessler, the McNeil Family Professor of Health Care Policy in the Blavatnik Institute at HMS, John McGrath, conjoint professor at UQ’s Queensland Brain Institute, and their colleagues from 27 other countries analyzed data collected between 2001 and 2022 as part of the WHO’s World Mental Health Survey Initiative, which is based at HMS.

“Mental disorders are a major health problem worldwide, with massive unmet need for treatment,” said Kessler, the principal investigator of the initiative.

“While many scalable interventions for prevention and treatment have been developed, allocation is often suboptimal. This study provides important insights that can help in targeting efforts to optimize the benefit of these interventions.” 

Who gets which illnesses?

The study showed that the most common mental illnesses were mood disorders, such as major depression or anxiety, and that the risk of certain mental disorders differed by sex.

The three most common mental health disorders among women were:

• Depression.
• Specific phobia, a disabling anxiety that interferes with daily life.
• Post-traumatic stress disorder, PTSD.

The three most common mental health disorders among men were:

• Alcohol abuse.
• Depression.
• Specific phobia.

Understanding how and when disorders arise

The researchers also found that mental health disorders typically first emerge in childhood, adolescence, or young adulthood. 

“By understanding the age at which these disorders commonly arise, we can tailor public health interventions and allocate resources to ensure that appropriate and timely support is available to individuals at risk,” Kessler said. 

The peak age of first onset was 15 years old, with a median age of onset of 19 for men and 20 for women, the study found. 

“This lends weight to the need to invest in basic neuroscience to understand why these disorders develop, as well as mental health services that have a particular focus on young people,” said McGrath, who was the study’s corresponding author.

“Services need to be able to detect and treat common mental disorders promptly, and be optimized to suit patients in these critical parts of their lives.”