The report says that's despite the fact that the burden of mental illness in the province is higher than that of all cancers combined and all infectious diseases combined.
Co-author Dr. Paul Kurdyak says that there would be a public outcry if the percentage of diabetes sufferers getting treatment was as low as the proportion of mental illness sufferers getting help.
The report, produced by Public Health Ontario and the Institute for Clinical Evaluative Sciences, says the overall burden of mental illness and addictions in Ontario is 1.5 times higher than that of all cancers and seven times higher than all infectious diseases.
"Approximately 60 to 65 per cent of people with depression and as many as 90 per cent of those with alcohol-use disorder remain untreated," says Kurdyak, chief of general and health systems psychiatry at the Centre for Addiction and Mental Health (CAMH).
"Yet there are effective therapies available for people suffering from these disorders."
Another co-author, Dr. Jurgen Rehm, said people don't seek care because of the stigma attached to these disorders, particularly for problematic alcohol use. Rehm is director of CAMH's Social and Epidemiological Research Department.
Note to readers: This is a corrected story. An earlier version said the report was produced by CAMH and the Institute for Clinical Evaluative Sciences (ICES). It was a joint undertaking of ICES and Public Health Ontario.