Adolescent marijuana use from 2002 to 2008: higher in states with medical marijuana laws, cause still unclear

Abstract

Purpose: Since 1996, 16 states have legalized marijuana use for medical purposes. The current study provides a scientific assessment of the association of medical marijuana laws (MML) and adolescent marijuana use using national data.

Method: State representative survey data on approximately 23,000 12-17 year olds were collected by the National Survey on Drug Use and Health annually from 2002-2008. Yearly state-specific estimates of prevalence of past-month marijuana use and perception of its riskiness were statistically tested for differences between states with and without MML by year and across years.

Results: States with MML had higher average adolescent marijuana use, 8.68% (95% CI: 7.95-9.42) and lower perception of riskiness, during the period 2002-2008 compared to states without MML, 6.94% (95% CI: 6.60-7.28%). In the eight states that passed MML since 2004, in the years prior to MML passage, there was already a higher prevalence of use and lower perceptions of risk in those states compared to states that have not passed MML.

Conclusions: While the most likely of several possible explanations for higher adolescent marijuana use and lower perceptions of risk in MML states cannot be determined from the current study, results clearly suggest the need for more empirically-based research on this topic.

Figure 1

Prevalence of past month marijuana use among 12 to 17 year olds in states with MML¹ (thick lines: solid after passing law, dashed before passing law) and states without MML (thin dotted lines). State abbreviation labels are noted along the left and right of the figure². ¹Eight states passed medical marijuana laws (MML) before 2002 (California CA in 1996; Oregon OR, Washington WA, and Alaska AK in 1998; Maine ME in 1999; Colorado CO, Nevada NV, and Hawaii HI in 2000) and are represented with solid thick lines from 2002–2008. Five states passed MML during the time period with NSDUH data available 2002–2008 (Montana MT and Vermont VT in 2004; Rhode-Island RI in 2006; New Mexico NM in 2007; Michigan MI in 2008) and 3 additional states passed MML after 2008 (New Jersey NJ and Arizona AZ in 2010; Delaware DE in 2011) and are represented with dashed thick lines before passage and solid thick lines after passage, if applicable (i.e. MI, NJ, AZ, and DE do not have after passage data available due to MML enacted in 2008 or later). ²Massachusettes MA and New Hampshire NH are labeled because of their high prevalence among states without MML