February 19, 2019
The systematic review and meta-analysis included 11 studies and more than 23,300 adolescents and teens. Results showed that the cannabis users were 37% more likely to develop depression in young adulthood than their non-using counterparts.
Similarly, the pooled odds ratios (ORs) for suicidal ideation and suicidal attempts were 1.50 and 3.46, respectively, for the adolescent cannabis users compared with non-users.
"Many studies have been previously published looking into the relationship between cannabis and things like depression, psychosis, schizophrenia, and cognitive disorder; but nobody has previously performed a meta-analysis where all these data were combined," principal investigator Gabriella Gobbi, MD, PhD, Department of Psychiatry, McGill University, Montreal, Quebec, Canada, told Medscape Medical News.
"This meta-analysis demonstrated the strong association between cannabis consumption in adolescence and depression, as well as suicidal ideation and suicidal attempt, in young adulthood," she added.
The findings were published online February 13 in JAMA Psychiatry.
World's Most Common Illicit Drug
Cannabis is the world's most commonly used illicit drug and enjoys significant popularity among American adolescents, the investigators note. Between 1991 and 2011, 20.9% of American adolescents reported using it in the previous month. In addition, about 7% of US high school seniors use cannabis daily or near-daily.
Despite its firm place in teen culture, regular cannabis use is associated with a host of negative consequences in this population, from impaired scholastic achievement to earlier onset of psychosis and neuropsychological decline.
Previous research has hypothesized that given the developing nature of the adolescent brain, psychotropic drug use may alter physiological neurodevelopment, especially of the frontal cortex and limbic system.
Although the effects of cannabis use have been the subject of considerable research, the current investigators note that no systematic review or meta-analysis has been performed that summarized the association between adolescent cannabis consumption and risk for depression in young adulthood.
Given this research shortfall, the researchers set out to systematically review and analyze a series of longitudinal prospective cohort studies. Each measured cannabis use during adolescence (≤ 18 years of age) and subsequently evaluated the risk for anxiety, depression, and suicidality during users' young-adult years (ages 18 to 32).
To do so, a variety of databases for all relevant clinical literature published through January 23, 2017 was searched. References of included studies and pertinent reviews were manually verified for other potential articles.
Two reviewers independently assessed potential articles, which were only included in the meta-analysis if they met a number of inclusion criteria. Of note, studies were only included if they comprised population-based data collected longitudinally and prospectively and included specific outcome measures related to depression, suicidal behavior, anxiety, or mixed anxiety-depressive symptoms. Cannabis use was measured in most trials using a self-reported questionnaire.
"All the studies we chose controlled for premorbid depression because we wanted to exclude the possibility that cannabis was being used as self-medication," Gobbi said.
After screening 3142 articles, 269 were selected for full-text review. The final cohort included 11 studies comprising 23,317 individuals in the quantitative analysis.
Public Health Implications
Seven studies were pooled to estimate the association between cannabis use during adolescence and development of depression in young adulthood. The pooled OR for depression among these individuals was a significant (OR, 1.37; 95% CI, 1.16 - 1.62).
After pooling three relevant studies, cannabis use during adolescence was also found to be associated with increased risk for developing anxiety in young adulthood, although it was not significant (OR, 1.18; 95% CI, 0.84 - 1.67).
Similarly, pooled results from three studies that measured the association with subsequent suicidal ideation in young adulthood yielded an OR of 1.50 (95% CI, 1.11 - 2.03). The OR for suicide attempt during young adulthood was 3.46 (95% CI, 1.53 - 7.84).
The findings could have significant public health implications, as they translate into more than 400,000 cases of adolescent depression that are potentially attributable to cannabis exposure, the authors note. As such, they stress the importance of educating teenagers regarding the risks of cannabis use.
"Given the likelihood of a window of risk during adolescence when the deleterious effects of cannabis are most pronounced, the findings in this meta-analysis suggest that cannabis is a serious public health concern and there is an urgent need to implement better drug use prevention programs targeting the use of cannabis among adolescents and interventions aimed at educating adolescents to develop the skills to resist peer pressure on drug consumption," they write.
Clinicians also need to consider cannabis use when evaluating young people, Gobbi added. "It's important when you evaluate a patient in their early 20s to evaluate also their consumption of cannabis, both past and present," she said.
Commenting on the research for Medscape Medical News, Anthony Levitt, MD, from the University of Toronto, Ontario, Canada, said the findings make a powerful statement about cannabis use, albeit one that researchers in the field have known for some time.
"The meta-analysis has compiled the wisdom that's grown over the last decade," said Levitt, who was not involved in the research.
"It's not news that cannabis is associated with increased risk of the onset of other mental illnesses, including psychosis and schizophrenia. So that it's associated with increased risk of depression is not surprising," he added.
The recent legalization of cannabis in many states has opened a Pandora's box for which the medical community is largely unprepared, Levitt noted.
"It's not a question of whether recreation cannabis use should or shouldn't be legalized," he said. "The medical issue is this substance is associated with significant impairment, both in terms of acute intoxication, as well as chronic use and the precipitation of mental illness, and all the sequelae of behaviors that come with addiction.
"And we are not prepared for the tsunami of problems that are going to arise as a result."
Part of the issue is that most adolescents believe cannabis is harmless, Gobbi added.
"Very often I talk in schools to present data about cannabis and many adolescents are not aware at all about its risks. They think that since cannabis is a plant, it poses no danger at all," she said.
The research was funded by the Canadian Institutes of Health Research and Quebec Network on Suicide, Mood Disorders, and Related Disorders. Although not related to the meta-analysis, Gobbi has previously received a grant for the study of cannabidiol in neuropathic pain by the Quebec Ministry of Economy, Science, and Innovation with the participation of Aurora Cannabis.