Sevigny Eric L, Pacula Rosalie Liccardo, Heaton Paul
Department of Criminology and Criminal Justice, University of South Carolina, 1305 Greene Street, Columbia, SC 29208, USA.
RAND Drug Policy Research Center, RAND Corporation, 1776 Main Street, P.O. Box 2138, Santa Monica, CA 90407-2138, USA.
Int J Drug Policy. 2014 Mar;25(2):308-19. doi: 10.1016/j.drugpo.2014.01.003. Epub 2014 Jan 18.
Marijuana potency has risen dramatically over the past two decades. In the United States, it is unclear whether state medical marijuana policies have contributed to this increase.
Employing a differences-in-differences model within a mediation framework, we analyzed data on n=39,157 marijuana samples seized by law enforcement in 51 U.S. jurisdictions between 1990 and 2010, producing estimates of the direct and indirect effects of state medical marijuana laws on potency, as measured by Δ(9)-tetrahydrocannabinol content.
We found evidence that potency increased by a half percentage point on average after legalization of medical marijuana, although this result was not significant. When we examined specific medical marijuana supply provisions, results suggest that legal allowances for retail dispensaries had the strongest influence, significantly increasing potency by about one percentage point on average. Our mediation analyses examining the mechanisms through which medical marijuana laws influence potency found no evidence of direct regulatory impact. Rather, the results suggest that the impact of these laws occurs predominantly through a compositional shift in the share of the market captured by high-potency sinsemilla.
Our findings have important implications for policymakers and those in the scientific community trying to understand the extent to which greater availability of higher potency marijuana increases the risk of negative public health outcomes, such as drugged driving and drug-induced psychoses. Future work should reconsider the impact of medical marijuana laws on health outcomes in light of dramatic and ongoing shifts in both marijuana potency and the medical marijuana policy environment.
在过去二十年里，大麻效力急剧上升。在美国，尚不清楚各州的医用大麻政策是否导致了这种上升。
我们在一个中介框架内采用双重差分模型，分析了1990年至2010年间美国51个司法管辖区执法部门查获的n = 39157份大麻样本数据，得出了各州医用大麻法律对效力（以Δ(9)-四氢大麻酚含量衡量）的直接和间接影响估计值。
我们发现有证据表明，医用大麻合法化后效力平均提高了0.5个百分点，尽管这一结果并不显著。当我们研究具体的医用大麻供应条款时，结果表明零售药房的合法许可影响最大，平均效力显著提高了约1个百分点。我们对医用大麻法律影响效力的机制进行的中介分析没有发现直接监管影响的证据。相反，结果表明这些法律的影响主要是通过高效力的无籽大麻在市场份额中的构成变化产生的。
我们的研究结果对政策制定者以及科学界那些试图了解更高效力大麻的更多可及性在多大程度上增加了负面公共卫生后果（如毒驾和药物性精神病）风险的人具有重要意义。鉴于大麻效力和医用大麻政策环境都在发生巨大且持续的变化，未来的工作应重新考虑医用大麻法律对健康结果的影响。
