Medical marijuana laws and adolescent marijuana use in the United States: a systematic review and meta‐analysis

Abstract

AimsTo conduct a systematic review and meta‐analysis of studies in order to estimate the effect of US medical marijuana laws (MMLs) on past‐month marijuana use prevalence among adolescents.MethodsA total of 2999 papers from 17 literature sources were screened systematically. Eleven studies, developed from four ongoing large national surveys, were meta‐analyzed. Estimates of MML effects on any past‐month marijuana use prevalence from included studies were obtained from comparisons of pre–post MML changes in MML states to changes in non‐MML states over comparable time‐periods. These estimates were standardized and entered into a meta‐analysis model with fixed‐effects for each study. Heterogeneity among the study estimates by national data survey was tested with an omnibus F‐test. Estimates of effects on additional marijuana outcomes, of MML provisions (e.g. dispensaries) and among demographic subgroups were abstracted and summarized. Key methodological and modeling characteristics were also described. Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) guidelines were followed.ResultsNone of the 11 studies found significant estimates of pre–post MML changes compared with contemporaneous changes in non‐MML states for marijuana use prevalence among adolescents. The meta‐analysis yielded a non‐significant pooled estimate (standardized mean difference) of −0.003 (95% confidence interval = −0.012, +0.007). Four studies compared MML with non‐MML states on pre‐MML differences and all found higher rates of past‐month marijuana use in MML states pre‐MML passage. Additional tests of specific MML provisions, of MML effects on additional marijuana outcomes and among subgroups generally yielded non‐significant results, although limited heterogeneity may warrant further study.ConclusionsSynthesis of the current evidence does not support the hypothesis that US medical marijuana laws (MMLs) until 2014 have led to increases in adolescent marijuana use prevalence. Limited heterogeneity exists among estimates of effects of MMLs on other patterns of marijuana use, of effects within particular population subgroups and of effects of specific MML provisions.

Correct knowledge of medical cannabis legal status in one's own state: Differences between adolescents and adults in the United States, 2004–2013

“…M. Anderson et al, 2014; Choi, 2014; Choo et al, 2014; Harper et al, 2012; D. S. Hasin et al, 2015; Johnson, 2015; Johnson et al, 2017; Keyes et al, 2016; Martins et al, 2016; Pacula et al, 2015; Sarvet et al, 2018; Smart, 2015; Wall et al, 2016; Wen et al, 2015). In contrast, four studies using large surveys and similar methodology found MCLs to be associated with increases in cannabis use among adults (Chu, 2014; D.…”

Changes over time in marijuana use, deviant behavior and preference for risky behavior among US adolescents from 2002 to 2014: testing the moderating effect of gender and age

“…These declines are part of a broader trend towards delayed adult activities (e.g. Declines in marijuana use, deviance and risk preference in youth are also occurring in the context of changing medical marijuana laws, which have not been causally related to changes in marijuana use in youth in a recent meta-analysis [47] or affected perceived availailability of marijuana use at ages 12-17 years [12]. These delays are often attributed to a greater parental investment (due to older age of childbearing and fewer children) [43,44], general economic prosperity prior to the Great Recession and a change in how adolescents interact due to technology, that allows interaction without unsupervised time alone with other adolescents, which is when deviant activities and experimentation with drug use often occur [45,46].…”

Medical cannabis in the UK

“…These fears are probably overblown, and not just because cannabis is far less lethal than opioids 18. Legalising medical marijuana, with relatively liberal access, has not caused major increases in cannabis use in the US 19. Indeed, there are some indications that it has reduced harms associated with opioid analgesics, including deaths from overdose and workplace or traffic injuries 202122…”