People aged 14 to 20 are more often being diagnosed with psychotic disorders, including schizophrenia, compared with those born earlier, a large Ontario study examining 30 years of data suggests.

To conduct the study, published in Monday’s issue of the Canadian Medical Association Journal (CMAJ), researchers looked at health administrative data from more than 12 million Ontario residents born between 1960 and 2009 to look for cases of a psychotic disorder.

In the Ontario study, those diagnosed with psychotic disorders not linked to mood disorders, such as schizophrenia, were more likely to be male, live in low-income neighbourhoods, be a long-standing resident of Canada and have received care for mental health disorders and substance use.

Why isn’t known. Myran and his co-authors suggest several possible reasons for the increases: older parental age, socioeconomic- and migration-associated stress and an increase in some negative childhood experiences like abuse in more recent decades.

Myran said there likely isn’t a single explanation, but he called substance use — including cannabis, stimulants, hallucinogens and synthetic drugs — a leading possibility contributing to the rising rates over 20 years.