A new study published in the journal Psychological Medicine found that adolescents who use cannabis have an eleven times higher risk of developing a psychotic disorder than those who do not use cannabis. This finding highlights the potential mental health risks associated with adolescent cannabis use, suggesting the association may be stronger than previously thought.
Cannabis, commonly known as marijuana, is a plant that has been used for medicinal and recreational purposes for thousands of years. It contains many chemical compounds called cannabinoids, with tetrahydrocannabinol (THC) being the best known for its psychoactive effects.
THC is the substance primarily responsible for the “high” users experience, as it interacts with the brain’s endocannabinoid system, influencing mood, perception, and various cognitive functions. Another major cannabinoid is cannabidiol (CBD), which is non-psychoactive and often touted for its potential therapeutic benefits.
The potency of cannabis, especially in terms of THC content, has increased significantly in recent decades. In the 1980s, the average THC content of cannabis was around 1%. However, due to selective breeding and advanced growing techniques, modern strains can contain THC levels above 20%, and some extracts can even exceed 90% THC.
This dramatic increase in potency has raised concerns among medical professionals about the risk of more serious and widespread adverse health effects, particularly among younger users whose brains are still developing.
“My interest in this topic was initially motivated by the legalization of recreational cannabis in Canada, which occurred largely in the absence of solid evidence on the risks of cannabis use,” said the author. of the study André McDonald, CIHR postdoctoral researcher at the Peter Boris Center. for Addiction Research and the Michael G. DeGroote Center for Medicinal Cannabis Research at McMaster University.
“One of the big questions related to cannabis is its link with psychotic disorders, particularly among young people. Most studies on this topic have used data from the 20th century, when cannabis was significantly less potent in terms of THC than it is today. So we were also curious if using more recent data would show a stronger link.
To conduct their study, researchers linked data from a demographic survey of more than 11,000 young people in Ontario, Canada, with health service utilization records. These records included hospitalizations, emergency department visits, and outpatient visits. Survey data came from the Canadian Community Health Survey (CCHS) cycles from 2009 to 2012, while health services data came from ICES.
The sample included non-institutionalized Ontario residents aged 12 to 24 years. To ensure the accuracy of their results, the researchers excluded respondents who had used health services for psychotic disorders in the six years before their survey interview. This exclusion was intended to reduce the risk of reverse causality, in which individuals may have initiated cannabis use to self-medicate for already existing psychotic symptoms.
Respondents were asked whether they had ever used cannabis and, if so, whether they had used it in the past 12 months. The primary outcome measured was time to first outpatient visit, first emergency department visit, or psychotic disorder-related hospitalization. The researchers also adjusted for various sociodemographic and substance use confounding factors to isolate the effect of cannabis use on the development of psychotic disorders.
Adolescents who reported using cannabis in the past year were eleven times more likely to be diagnosed with a psychotic disorder than non-users. Interestingly, this elevated risk was not observed among young adults aged 20 to 24, indicating that adolescence is a particularly vulnerable time for the mental health effects of cannabis.
The data also showed that among adolescents diagnosed with a psychotic disorder, the vast majority had a history of cannabis use. More precisely, approximately 5 out of 6 adolescents hospitalized or consulted in the emergency room for a psychotic disorder had already reported having used cannabis. This finding supports the neurodevelopmental theory that the adolescent brain is particularly sensitive to the effects of cannabis, which can disrupt normal brain development and increase the risk of serious mental health problems.
“People should be aware of the risks associated with cannabis use from a young age. This study estimates that adolescents who use cannabis are at 11 times greater risk of developing a psychotic disorder than adolescents who do not use cannabis,” McDonald told PsyPost.
“It is important to recognize that the vast majority of people who use cannabis will not develop a psychotic disorder, but this study suggests that most adolescents who develop a psychotic disorder have a history of cannabis use. This is important information to convey to teenagers, but also to parents of teenagers, who may not know that today’s cannabis products are different and may be more harmful than those that existed when they were teenagers. »
Although the study provides compelling evidence of a strong link between adolescent cannabis use and psychotic disorders, it still has some limitations. The potential for reverse causality remains, as early symptoms of psychosis could lead some adolescents to use cannabis as a form of self-medication before seeking formal medical help. Additionally, the study could not take into account genetic predispositions, family history of mental health problems, or trauma – all factors that could influence both cannabis use and risk of psychotic disorders.
Nonetheless, the findings reinforce concerns about early cannabis use.
“As marketed cannabis products have become more widely available and have higher THC content, the development of prevention strategies targeting adolescents is more important than ever,” said lead author Susan Bondy, a scientist affiliated with ICES and associate professor at the University of Toronto’s Dalla Lana School of Public Health.
McDonald added: “Young Canadians are among the heaviest consumers of cannabis in the world. If we follow the precautionary principle, the bottom line is that more needs to be done to prevent early use of cannabis.
The study titled “Age-dependent association of cannabis use and risk of psychotic disorder” was authored by André J. McDonald, Paul Kurdyak, Jürgen Rehm, Michael Roerecke and Susan J. Bondy.