Study reveals rising psychosis rates among younger generations

People born more recently are being diagnosed with psychotic disorders (e.g., schizophrenia) more often and at younger ages than people born earlier, suggests a large study of more than 12 million people in Ontario, published in CMAJ (Canadian Medical Association Journal) https://www.cmaj.ca/lookup/doi/10.1503/cmaj.250926.

"Individuals with psychotic disorders face substantial morbidity and risk of premature death, and often require substantial health services and social support," writes Dr. Daniel Myran, Gordon F. Cheesbrough Research Chair in Family and Community Medicine, North York General, and a scientist at ICES and the Bruyère Health Research Institute, with coauthors. "Consequently, the observed trends raise important questions about possible causes and consequences of increasing numbers of psychotic disorder diagnoses."

The study, conducted by researchers from ICES, North York General, Ottawa Hospital Research Institute, and Bruyère Health Research Institute, included 12.2 million people born in Ontario between 1960 and 2009, of whom 152 587 were diagnosed with a psychotic disorder, such as schizophrenia. Over the study, in people aged 14 to 20 years, rates of new cases increased by 60% (62.5 to 99.7 cases per 100 000) between 1997 and 2023. The increases occurred in more recent birth cohorts, with rates of new cases beginning to increase for those born in the 1980s and later. For example, individuals born in 2000 to 2004 were estimated to have a 70% greater rate of new diagnoses of psychotic disorders compared with those born in 1975 to 1979. The total number of people diagnosed with a psychotic disorder by the time they reached age 30 increased by 37.5% for those born in 1990 to 1994 compared with those born in 1975 to 1979.

Increases in psychosis over time were consistent for both males and females, though males remained at higher risk over the study period. Those diagnosed with a nonaffective psychotic disorder - meaning 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.

Evidence is limited on birth cohort changes in psychotic disorders, but two recent studies from Denmark and Australia also found increases over time in schizophrenia diagnoses in younger individuals. This study contributes to the evidence on this important topic.

The authors suggest several reasons for these increases. Older parental age, socioeconomic- and migration-associated stress, and some negative childhood experiences have increased in younger birth cohorts. Substance use may also be contributing to these rising rates.

"We don't yet know what's driving these changes, and it's likely there isn't a single explanation. Understanding what's behind this trend will be critical to prevention and early support," says Dr. Myran. "A leading possibility is substance use - including cannabis, stimulants, hallucinogens, and synthetic drugs. The use of substances, especially earlier in life, is associated with the development and worsening of psychotic disorders, and substance use in Canada has risen over the past two decades."

The authors call for more research into what underlies these increased rates of psychosis and variability in age cohorts.