Source: University of Montreal.
An UdeM study confirms the link between marijuana use and psychotic-like experiences in a Canadian adolescent cohort.
Going from an occasional user of marijuana to a weekly or daily user increases an adolescent’s risk of having recurrent psychotic-like experiences by 159%, according to a new Canadian study published today in the Journal of Child Psychology and Psychiatry. The study also reports effects of marijuana use on cognitive development and shows that the link between marijuana use and psychotic-like experiences is best explained by emerging symptoms of depression.
“To clearly understand the impact of these results, it is essential to first define what psychotic-like experiences are: namely, experiences of perceptual aberration, ideas with unusual content and feelings of persecution,” said the study’s lead author, Josiane Bourque, a doctoral student at Université de Montréal’s Department of Psychiatry. “Although they may be infrequent and thus not problematic for the adolescent, when these experiences are reported continuously, year after year, then there’s an increased risk of a first psychotic episode or another psychiatric condition.”
She added: “Our findings confirm that becoming a more regular marijuana user during adolescence is, indeed, associated with a risk of psychotic symptoms. This is a major public-health concern for Canada.”
What are the underlying mechanisms?
One of the study’s objectives was to better understand the mechanisms by which marijuana use is associated with psychotic-like experiences. Bourque and her supervisor, Dr. Patricia Conrod at Sainte Justine University Hospital Research Center hypothesized that impairments in cognitive development due to marijuana misuse might in turn exacerbate psychotic-like experiences.
This hypothesis was only partially confirmed, however. Among the different cognitive abilities evaluated, the development of inhibitory control was the only cognitive function negatively affected by an increase in marijuana use. Inhibitory control is the capacity to withhold or inhibit automatic behaviours in favor of a more contextually appropriate behaviour. Dr. Conrod’s team has shown that this specific cognitive function is associated with risk for other forms of substance abuse and addiction.
“Our results show that while marijuana use is associated with a number of cognitive and mental health symptoms, only an increase in symptoms of depression – such as negative thoughts and low mood – could explain the relationship between marijuana use and increasing psychotic-like experiences in youth,” Bourque said.
These findings have important clinical implications for prevention programs in youth who report having persistent psychotic-like experiences. “While preventing adolescent marijuana use should be the aim of all drug strategies, targeted prevention approaches are particularly needed to delay and prevent marijuana use in young people at risk of psychosis,” said Patricia Conrod, the study’s senior author and a professor at UdeM’s Department of Psychiatry.
Conrod is optimistic about one thing, however: the school-based prevention program that she developed, Preventure, has proven effective in reducing adolescent marijuana use by an overall 33%. “In future programs, it will be important to investigate whether this program and other similar targeted prevention programs can delay or prevent marijuana use in youth who suffer from psychotic-like experiences,” she said. “While the approach seems promising, we have yet to demonstrate that drug prevention can prevent some cases of psychosis.”
A large youth cohort from Montreal
The study’s results are based on the CIHR-funded Co-Venture project, a cohort of approximately 4,000 adolescents aged 13 years old from 31 high schools in the Greater Montreal area. These teens are followed annually from Grade 7 to Grade 11. Every year they fill out computerized questionnaires to assess substance use and psychiatric symptoms. The teens also complete cognitive tasks to allow the researchers to evaluate their IQ, working memory and long-term memory as well as their inhibitory control skills.
To do their study, the research team first confirmed results from both the United Kingdom and Netherlands showing the presence of a small group of individuals (in Montreal, 8%) among the general population of adolescents who report recurrent psychotic-like experiences. Second, the researchers explored how marijuana use between 13 and 16 years of age increases the likelihood of belonging to the 8%. Finally, they examined whether the relationship between increasing use of marijuana and increasing psychotic-like experiences can be explained by emerging symptoms of anxiety or depression, or by the effects of substance use on developing cognitive abilities.
Funding: This study was funded by a Canadian Institutes of Health Research (CIHR) doctoral fellowship to Josiane Bourque, a Fond de recherche du Québec – Santé senior investigator award to Patricia Conrod, and a CIHR grant to Patricia Conrod and co-investigators.
Source: Mélanie Dallaire – University of Montreal
Image Source: NeuroscienceNews.com image is adapted from the UM news release.
Original Research: Abstract for “Cannabis use and psychotic-like experiences trajectories during early adolescence : the coevolution and potential mediators,” by Josiane Bourque, Mohammad H. Afzali, Maeve O’Leary-Barrett and Patricia Conrod in Journal of Child Psychology and Psychiatry. Published online July 5 2017 doi:10.1111/jcpp.12765
Cannabis use and psychotic-like experiences trajectories during early adolescence : the coevolution and potential mediators,
The authors sought to model the different trajectories of psychotic-like experiences (PLE) during adolescence and to examine whether the longitudinal relationship between cannabis use and PLE is mediated by changes in cognitive development and/or change in anxiety or depression symptoms.
A total of 2,566 youths were assessed every year for 4-years (from 13- to 16-years of age) on clinical, substance use and cognitive development outcomes. Latent class growth models identified three trajectories of PLE: low decreasing (83.9%), high decreasing (7.9%), and moderate increasing class (8.2%). We conducted logistic regressions to investigate whether baseline levels and growth in cannabis use were associated with PLE trajectory membership. Then, we examined the effects of potential mediators (growth in cognition and anxiety/depression) on the relationship between growth in cannabis use and PLE trajectory.
A steeper growth in cannabis use from 13- to 16-years was associated with a higher likelihood of being assigned to the moderate increasing trajectory of PLE [odds ratio, 2.59; 95% confidence interval (CI), 1.11–6.03], when controlling for cumulative cigarette use. Growth in depression symptoms, not anxiety or change in cognitive functioning, mediated the relationship between growth in cannabis use and the PLE moderate increasing group (indirect effect: 0.07; 95% CI, 0.03–0.11).
Depression symptoms partially mediated the longitudinal link between cannabis use and PLE in adolescents, suggesting that there may be a preventative effect to be gained from targeting depression symptoms, in addition to attempting to prevent cannabis use in youth presenting increasing psychotic experiences.
“Cannabis use and psychotic-like experiences trajectories during early adolescence : the coevolution and potential mediators,” by Josiane Bourque, Mohammad H. Afzali, Maeve O’Leary-Barrett and Patricia Conrod in Journal of Child Psychology and Psychiatry. Published online July 5 2017 doi:10.1111/jcpp.12765