The most common conditions associated with mental illness are depression and anxiety disorders, the study said. And at least a quarter of the global population were thought to experience these conditions over the course of their lifetime.
Researchers at the GHC also said that mental illness was a "major block" on the global economy as it was found to be the main illness among people of a working age. Therefore, treating the conditions, it said, would save national income per head by 5 percent — that equates to billions worldwide.
The study estimated that for every $1 spent on treating depression, production would be restored by the equivalent of $2.50. And while physical healthcare costs were thought to balance out, the GHC claimed net savings when treating anxiety disorders was greatest of all — with production restored by the equivalent of $3 for every $1 spent.
In the U.K., the National Health Service (NHS) estimates that around 10 to 15 percent of people are considered to have had a mental illness at some stage of their lives.
There are many types of mental illness but most conditions fit into either a neurotic or psychotic category, according to the NHS.