Colorado legalized marijuana for recreational use and stores opened January 1, 2014. They are widespread in the state.

In 2014 and 2015, heroin overdose deaths in Colorado continued to increase over prior years. Among Colorado men, heroin overdose deaths in 2014 increased 31% over 2013. Among women, 16%.

http://gazette.com/overdosing-on-heroin-use-deaths-surge-in-...

Marijuana legalization does not appear to be a panacea to opiod abuse. Recreational marijuana use has a very different origin than prescription painkiller addiction (which often begins with usage to manage real pain, but spins into an addiction that then turns to heroin when the pills become too expensive).