Teen Cannabis Use Tied to Dramatic Increased Psychosis Risk

Teenagers who use cannabis have a dramatic increased risk for a psychotic disorder compared with their counterparts who don’t use the drug, new research showed.

Investigators at the University of Toronto, The Centre for Addiction and Mental Health (CAMH), and the Institute for Clinical Evaluative Sciences (ICES), in Canada, linked recent population-based survey data from over 11,000 youngsters to health service use records, including hospitalizations, emergency department (ED) visits, and outpatient visits.

“We found a very strong association between cannabis use and risk of psychotic disorder in adolescence [although] surprisingly, we didn’t find evidence of association in young adulthood,” lead author André J. McDonald, PhD, currently a postdoctoral fellow at the Peter Boris Centre for Addictions Research and the Michael G. DeGroote Centre for Medicinal Cannabis Research, McMaster University, Hamilton, Ontario, Canada, said in a news release.

“These findings are consistent with the neurodevelopmental theory that teens are especially vulnerable to the effects of cannabis,” said McDonald, who conducted the research.

The study was published online on May 22 in Psychological Medicine.

Increased Potency

“Epidemiologic research suggests that cannabis use may be a significant risk factor for psychotic disorders,” the authors wrote. However, methodological limitations of previous studies make it difficult to estimate the strength of association, with the current evidence base relying largely on cannabis use during the twentieth century, when the drug was “significantly less potent.” It’s plausible that the strength of association has increased due to increased cannabis potency.

The researchers believe youth cannabis use and psychotic disorders is “a critical public health issue,” especially as more jurisdictions liberalize cannabis use and the perception of harm declines among youth.

To estimate the association between cannabis use during youth and the risk for a psychotic disorder diagnosis, using recent population-based data, they used data from the 2009 to 2012 cycles of the Canadian Community Health Survey (CCHS) linked to administrative health data at ICES to study noninstitutionalized Ontario residents, age 12-24 years, who had completed the CCHS during that period.

They excluded respondents who used health services for psychotic disorders during the 6 years prior to their CCHS interview date.

Respondents (n = 11,363; 51% men; mean age [SD], 18.3 [15.2-21.3] years) were followed for 6-9 years, with days to first hospitalization, ED visit, or outpatient visit related to a psychotic disorder as the primary outcome.

The researchers estimated age-specific hazard ratios during adolescence (12-19 years) and young adulthood (20-33 years) and conducted sensitivity analyses to explore alternative model conditions, including restricting the outcome to hospitalizations and ED visits, to increase specificity.

Compared with no cannabis use, cannabis use was significantly associated with an 11-fold increased risk for psychotic disorders during adolescence, although not during young adulthood (adjusted hazard ratio [aHR], 11.2; 95% CI, 4.6-27.3 and aHR, 1.3; 95% CI, 0.6-2.6, respectively).

Perception of Harm Declining

When the researchers restricted the outcome to hospitalizations and ED visits only, the strength of association “increased markedly” during adolescence, with a 26-fold higher association in cannabis users than in nonusers (aHR, 26.7; 95% CI, 7.7-92.8). However, there was no meaningful change during young adulthood (aHR, 1.8; 95% CI, 0.6-5.4).

“Many have hypothesized that adolescence is a more sensitive risk period than adulthood for the effect of cannabis use on psychotic disorder development, yet prior to this study, little epidemiologic evidence existed to support this view,” the authors wrote.

The data also suggest that cannabis use is “more strongly associated with more severe psychotic outcomes, as the strength of association during adolescence increased markedly when we restricted the outcome to hospitalizations and ED visits (the most severe types of health service use),” the investigators noted.

The authors noted several limitations. For instance, it’s unclear to what extent unmeasured confounders including genetic predisposition, family history of psychotic disorders, and trauma might have biased the results. In addition, they could not assess the potential confounding impact of genetic predisposition to psychotic disorders. The possibility of reverse causality also cannot be ruled out. It’s possible, they noted that individuals with “psychotic dispositions” may self-medicate or show greater disposition to cannabis use.

Moreover, the dataset neither captured important factors regarding the cannabis itself, including delta-9-tetrahydrocannabinol potency, mode of use, product type, or cannabis dependence, nor captured institutionalized and homeless youth.

Nevertheless, they pointed to the findings as supporting a “precautionary principle” — as more jurisdictions move to liberalize cannabis use and perception of harm declines among youth, the findings suggest that evidence-based cannabis prevention strategies for adolescents are warranted.

This study was supported by CAMH, the University of Toronto, and ICES, which is funded by an annual grant from the Ontario Ministry of Health and the Ministry of Long-Term Care. The authors declared no relevant financial relationships.

Batya Swift Yasgur, MA, LSW, is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape Medical News and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom (the memoir of two brave Afghan sisters who told her their story).