As of April 2017, 8 states and the District of Columbia have legalized recreational marijuana, but studies on the effects of legalization are limited. This study focuses on the effects of the regulation of marijuana sale on public health in Colorado’s counties. Certain counties in Colorado allow businesses to sell marijuana, while others do not. If alcohol and marijuana are economic substitutes, violent crime and traffic fatalities should be reduced. I find that the counties that allow retail marijuana dispensaries see a significant decrease in violent crime and unemployment for the first two years of legalization. My results also suggest these counties see a reduction in alcohol related traffic fatalities, but these results are not statistically significant by conventional methods.