Marijuana and the Teenage Brain

481552311Whatever your feelings on the rapid decriminalization of marijuana nationally as well as its meteoric rise as a cash crop, a study in this week's Lancet Psychiatry raises some red flags with regard to the use of this drug by adolescents.  As Rick and I discuss on PodMed this week, we second concerns as well as recommendations made by the authors of this study that for this group of vulnerable people, strict limits should be employed to reduce long term sequelae of marijuana use.

Investigators did a meta analysis of three longitudinal studies taking place in New Zealand and Australia, together comprising several thousand subjects followed from 13 to 30 years of age. Multiple assessments were made during the study period, but for the purposes of this analysis the relevant ones included cannabis use before the age of 17 years, with categories of never, less than monthly, monthly or more, weekly or more, or daily. Developmental outcomes to the age of 30 years included attainment of a high school degree, attainment of a university degree, dependence on cannabis, use of other illicit drugs, suicide attempt(s), depression, and welfare dependence.

The studies attempted to correct for a multitude of variables and confounders that may have impacted marijuana use and outcomes.  Here's what the paper states, "We included 53 covariate factors from the three studies in the analysis. These covariates spanned individual background and functioning, and measures of parental and peer factors... After adjustment, the associations for depression and welfare dependence were both non-significant and negligible in size. For all other outcomes the associations remained significant. The estimates for adjusted ORs [odds ratios] suggested that individuals who were daily users before age 17 years had odds of high-school completion and degree attainment that were 63% and 62% lower, respectively, than those who had never used cannabis; furthermore, daily users had odds of later cannabis dependence that were 18 times higher, odds of use of other illicit drugs that were eight times higher, and odds of suicide attempt that were seven times higher. Wow.  No matter how you spin that data, it's pretty powerful.  Moreover, the analysis identified a clear dose-response between deleterious outcomes and frequency of marijuana use.

What is it that makes marijuana use especially problematic for adolescents?  Evidence has been abundant for some time that adolescents undergo a period of neuronal sprouting and subsequent pruning that may account for their oft-observed impulsive behavior, and that seems to give way to a greater degree of sense as individuals age into their twenties and beyond. Perhaps the presence of metabolites of cannibis in the central nervous system hinders this process somehow.  Another explanation is that there is already some proclivity among those prone to choose cannibis use that accounts for the apparent sequelae.  In any case here's what we know:  there won't be a prospective trial anytime soon enrolling lots of teenagers and randomizing them to various frequencies of cannabis use or not, then looking at outcomes.  For now, we agree with the authors of the paper that both efforts to limit the availability of marijuana to teenagers as well as screening efforts should be employed, as we are all vested in the outcome.

Other topics this week include new hip and knee prostheses in BMJ, questionable medication use in people with profound dementia in JAMA Internal Medicine, and aspirin to prevent preeclampsia in Annals of Internal Medicine.  Until next week, y'all live well.



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