Do medical marijuana laws increase marijuana use? Replication study and extension.

Area of Science:

• Public Health
• Epidemiology
• Substance Use Research

Background:

• Prior studies suggested a correlation between medical marijuana laws (MMLs) and increased adolescent marijuana use.
• Concerns exist regarding potential confounding variables and measurement error in these previous findings.

Purpose of the Study:

• To replicate and extend previous research on the association between MMLs and adolescent marijuana use.
• To account for unmeasured state characteristics and measurement error in the analysis.
• To determine the causal effect of MMLs on adolescent marijuana use.

Main Methods:

• Utilized state-level marijuana use data from the National Survey on Drug Use and Health (2002-2009).
• Employed 2-sample t-tests and random-effects regression for replication.
• Applied difference-in-differences regression and simulations to address confounding and measurement error.

Main Results:

• Replicated previous findings of higher marijuana use in states with MMLs.
• Difference-in-differences models indicated a small decrease in past-month adolescent use (0.53 percentage points) post-MMLs.
• Models adjusted for measurement error showed minimal evidence of MMLs impacting marijuana use.

Conclusions:

• Adjusting for unmeasured state characteristics and measurement error significantly altered estimates of MMLs' impact.
• Found limited evidence supporting a causal relationship between MMLs and reported adolescent marijuana use.