A recent study published by the Royal Economic Society shows that there may be a link between some states passing medical marijuana laws and decreased violence associated with Mexican drug cartels. This appears to be especially stronger in border states.
The Free Beacon reports:
To determine the effect of medical marijuana laws on violent crime rates, the study authors performed three comparisons: They studied crime rates in counties before and after the introduction of medical marijuana; then between counties with and without medical marijuana; and finally, between counties at the border and further inland.
Combining these conclusions results in a reduction of 12.5 percent in the violent crime rate for border counties. Analysis using an alternate data set produced even more stark declines in violence: medical marijuana has "lead to a 40.6 percent decrease in drug-law related homicides in Mexican border states," the study says.
"We find that when a neighbour to a Mexican border state passes a MML [medical marijuana law], this results in a significant reduction in violent crime rates in the border state. More generally, we find that when a state passes a MML this reduces crime rates in the state in which the nearest Mexican border crossing is located. This evidence is consistent with our hypothesis that MMLs lead to a reduction in demand for illegal marijuana, followed by a reduction in revenue for Mexican DTOs, and, hence, a reduction in violence in the Mexican-border area," the study concludes.
You can read the full study here.