Gobbi, G. et al. (2019)
JAMA Psychiatry

While the impact of pre-teen and adolescent cannabis use on the development of psychosis has been investigated in depth, it’s not well understood how youth cannabis use impacts mood and suicidality in young adulthood. This systematic review and meta-analysis looked at 11 studies and 23,317 individuals to estimate the extent to which cannabis use during adolescence (under 18 years of age) is associated with the risk of developing subsequent major depression, anxiety, and suicidal behaviour in early adulthood (18 to 32 years of age). ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
After analyzing each study, the researchers found that the odds ratio (OR) of developing depression for cannabis users compared to nonusers was 1.37 (i.e., 1.37x more likely). The OR for suicidal ideation was 1.50, and for suicide attempts was an astounding 3.46. However, the pooled OR for anxiety was not statistically significant (1.18). ⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
Although the risk levels here remain moderate-to-low, they are still significant findings for how we treat youth cannabis use from a public health perspective. However, it’s important to point out a few things. 1) The researchers did not control for dosage. 2) Correlation doesn’t imply causation. What we have here is an association between two phenomena, and nothing more. 3) This may be an indirect correlation, as people with depression may see more value in using substances for self-medication purposes.