Mental health disorders are on the horizon for one in two people by the age of 75 after findings from an Australian co-led study spanning 29 countries.

Researchers from the University of Queensland, in partnership with Harvard medical school, studied data from face-to-face interviews of more than 150,000 adults across nearly 30 countries.

The data was collected over a 21-year period via the World Health Organisation's World mental health survey initiative and found a high prevalence of mental health issues and disorders.

Some 50 per cent of the population will develop at least one mental health disorder by the age of 75, lead author Professor John McGrath said.

"The most common were mood disorders such as major depression or anxiety," he said.

"We also found the risk of certain mental disorders differed by sex."

Among men, the most common mental health issues were alcohol abuse, depression and a specific phobia.

Among women, specific phobia and depression were prevalent as was post-traumatic stress disorder.

Researchers also unearthed mental health disorders typically first emerging in childhood, adolescence or young adulthood.

"The peak age of first onset was at 15 years old, with a median age of onset of 19 for men and 20 for women," Prof McGrath said.

"This lends weight to the need to invest in basic neuroscience to understand why these disorders develop."

Targeted programs and services for young people must be a priority, Harvard's Professor Ronald Kessler said.

"Services need to be able to detect and treat common mental disorders promptly, and be optimised to suit patients in these critical parts of their lives," he said.

"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."

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