Cannabis use in teens increases risk of depression
Geoff A. Modest, M.D.
Wed 2/20/2019 8:01 AM
A recent systematic review/meta-analysis looked at the association between cannabis use in adolescence and the subsequent risk of depression, anxiety, and suicidality in young adulthood (see marijuana subseq depression jamapsych2019 in dropbox, or doi:10.1001/jamapsychiatry.2018.4500).
Details:
-- 11 studies were found with 23,317 individuals assessing cannabis use in those younger than age 18 and the subsequent development of depression between the ages 18 to 32
Results:
--after adjusting for baseline depression, anxiety, and suicidality:
-- depression: cannabis users had 37% higher likelihood of depression, OR 1.37 (1.16-1.62)
-- notably, of the eight studies looking specifically at depression, every one of them found an increased trend with cannabis use, though only two studies individually found a statistically significant relationship
-- anxiety: nonsignificant 18% increase, OR 1.18 (0.84-1.67)
-- suicidal ideation: 50% increase risk, OR 1.50 (1.11- 2.03)
-- suicide attempt: 2 ½ times increased risk, OR 3.46 (1.57-7.84)
-- notably, of the three studies looking at suicide attempts, all were statistically significantly related with cannabis use; in terms of suicide ideation only one of three was significantly associated with cannabis use, the other two showing a trend to the association
-- of note, on further analysis there was no evidence that using structured diagnostic tools or scales to assess depression affected the above results
Commentary:
-- cannabis is the most widely used illicit drug, 3.8% of the global population had used it in the last year
-- the percentage of individuals 18 to 29 in the US who reported using cannabis in the last year increased from 10.5% in 2001-2 to 21.2% 2012-13
-- US adolescents from 1991-2011: 20.9% reported using cannabis in the past month, and 7% of US high school seniors used cannabis daily or near-daily
-- in the European Union: 87.6 million adults aged 15 to 64 (26.3% of this age group) tried cannabis during their lives
-- depression is also quite common in the United States: during 2013 to 16, 8.1% of individuals older than 20 experienced depression in a given two-week period.
-- cannabis use in adolescence has been associated with: diminished scholastic achievement, lower degree attainment and school abandonment, liability to addiction, earlier onset of psychosis, a dose-response curve to the development of psychosis (with increased risk among those taking the highest potency and highest frequency of cannabis), neuropsychological decline, increased motor vehicle crashes, adverse outcome in the offspring of mothers who smoke (eg low birth weight), worse respiratory symptoms and more frequent chronic bronchitis. see blog noted below
-- the concern about cannabis use in adolescents is heightened by the fact that the brain is most plastic at that time, with evidence of increased plasticity til about age 21. Many MRI studies have shown that people consuming higher doses at earlier ages have more volume loss in several important areas of the brain: hippocampus, amygdala, prefrontal cortex, as well as in the nucleus accumbens. see http://gmodestmedblogs.blogspot.com/2019/02/e-cigs-nicotine-as-gateway-drug.html , for the role of the nucleus accumbens in addiction. the hippocampus is associated with the development of long-term memory, and also has a role in spacial navigation; the amygdala has a role in emotions, mood, depression/anxiety, survival instincts and memory; the prefrontal cortex has a role in executive function, complex cognitive behavior, personality expression, and decision-making (and deficiencies are associated with more impulsive behavior). so, lots of really important areas not to lose volume....
-- as emphasized by the researchers, the effect size of the relationship between cannabis use in adolescence and depression is small. However, given the huge absolute number of teens using cannabis products (and increasing leaps and bounds, likely moreso with legalization in many areas), that small effect size likely translates to very large numbers of people: in this study they estimate that 413,326 adolescent cases of depression are potentially attributable to cannabis
-- the increased association with suicide attempts versus suicidal ideation is not so surprising, since the risk factors for each are somewhat different. In particular, suicide ideation is more closely tied with depression, whereas suicide attempts are more broadly related to mental illness (e.g. panic disorders, PTSD, bipolar disease, etc.) see https://www2.psych.ubc.ca/~klonsky/publications/AnnualReview2016.pdf
-- other studies not included in this meta-analysis confirmed the above relationship, some differentiating by patterns of cannabis usage. One study of 1232 first year college students did find differences in an array of adverse outcomes, with non-users faring significantly better; in particular, both the Beck Depression and Anxiety inventories were the worst for chronic marijuana users (see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390463/ ). Other studies found that higher risk of depression and anxiety in adolescents who continued to smoke until age 29.
-- Limitations of the study include the inherent limitations of meta-analyses and combining disparate studies with different inclusion/exclusion criteria and methodologies, inability to assess the granular individual patient data, combining data that use different depression scales and cutpoints, lack of quantitation of actual cannabis potency (which has generally increased lots since 1980). and, of course, as a review of observational studies even with long followup, these cannot not imply causation (just association). were there underlying psych issues in those choosing to use cannabis products years prior to their psych diagnosis?? and, perhaps these psych issues were not actually affected by the cannabis?? not able to say with any certainty without a randomized controlled trial, which undoubtedly will never happen
so, this meta-analysis adds to the litany of articles coming out about the adverse effects of cannabis on both physical and mental health. the concern, as with the recent blogs on e-cigarettes (eg, see http://gmodestmedblogs.blogspot.com/2019/02/e-cigs-nicotine-as-gateway-drug.html ), is that both cannabis and e-cigs are becoming more readily available, are of significantly higher potency than previously, are available in many seductive flavors/varieties, and are more legal/accepted/normalized than before
see http://gmodestmedblogs.blogspot.com/2018/11/marijuana-abstinence-improves-memory-in.html , which reviews a study finding that subsequent cannabis abstention was associated with improved memory function in teens
see http://gmodestmedblogs.blogspot.com/2016/12/teen-drug-use-in-us-new-survey.html which reviews drug use in teens, with numbers/comments on the increase in marijuana use
see http://gmodestmedblogs.blogspot.com/2016/12/teen-drug-use-in-us-new-survey.html for epigenetic effects of marijuana on rats (surprisingly to me that it was then inherited to the next generation)
http://gmodestmedblogs.blogspot.com/2014/06/marijuana-adverse-effects-review.html for a review of the adverse effects of marijuana
geoff
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