Cannabis consumption among adolescents associated with depression in adulthood
A recent meta-analysis showed that cannabis consumption in adolescence is associated with an increased risk of developing major depression, suicidality, and suicidal ideation in young adulthood.
The study involved analysis of 11 longitudinal prospective trials (n=23,317) assessing cannabis use in adolescents younger than 18 years of age, followed by assessment of development of depression in young adulthood (age 18 to 32 years). [JAMA Psychiatry 2019, doi: 10.1001/jamapsychiatry.2018.4500]
Results revealed that cannabis users had a 37 percent increased risk of developing depression in young adulthood compared with nonusers (odds ratio [OR], 1.37; 95 percent confidence interval [CI], 1.16 to 1.62; I2 = 0 percent).
“Although the causes of major depressive disorder are multifactorial and complex, this meta-analysis suggests that cannabis exposure could be a factor contributing to depression in young adulthood,” the authors of the study commented.
“In this study, the estimated population attributable risk is 7.2 percent, which translates to around 413,326 adolescent cases of depression potentially attributable to cannabis exposure,” added the authors.
The analysis also showed that cannabis use during adolescence is associated with increased odds of developing anxiety (OR, 1.18; 95 percent CI, 0.84 to 1.67; I2 = 42.0 percent), suicidal ideation (OR, 1.50; 95 percent CI, 1.11 to 2.03; I2 = 0 percent) and suicidal attempts (OR, 3.46; 95 percent CI, 1.53 to 7.84; I2 = 61.3 percent) during young adulthood.
No association was found between the country in which the study was conducted and the reported OR for depression in young adulthood. The pooled OR among studies carried out in the US (OR, 1.54; 95 percent CI, 1.20 to 1.98) was not significantly different vs those of other countries (OR, 1.24; 95 percent CI, 0.99 to 1.56).
“The effect size is modest, but considering that more than 20 percent of adolescents in the US report monthly use of cannabis, the consequences of cannabis use during adolescence are magnified in young adulthood,” the authors commented.
“This study is also consistent with past studies on brain imaging, which demonstrated the negative influence of cannabis on brain plasticity during its development. The brain remains in a state of active, experience-guided development from the prenatal period through childhood and adolescence until the age of approximately 21 years,” they added. [Nat Neurosci 1999;2:861-863; Trends Cogn Sci 2015;19:558-566]
Limitations of the study include the lack of causal inference analysis methods for individual patient data and the lack of adjustments made for other drugs of abuse or other psychosocial factors that may also be linked to depression and early cannabis consumption.
Cannabis is the world’s most widely used illicit drug, with 3.8 percent of the global population having used cannabis in 2016. [https://www.unodc.org/wdr2017/index.html] Among US adolescents surveyed from 1991 to 2011, the prevalence of cannabis use was high, with 20.9 percent reporting use in the past month, and about 7 percent of high school seniors reporting cannabis use daily or almost daily. [Adolesc Health 2014;55:160-166; http://www.monitoringthefuture.org/pubs/monographs/mtf-overview2012.pdf]