Probably unrelated to marijuana. See [1]. In Colorado, opioid overdose deaths decreased 6% in 2016. But heroin overdose deaths went up 22%. This followed a state effort to cut down on opioid prescriptions. The number of high-dose opioid prescriptions for more than 30 days was cut in half from 2015 to 2016.

Overview of heroin boom in Colorado: [2]

[1] https://www.colorado.gov/pacific/sites/default/files/Opioid%...

[2] https://localtvkdvr.files.wordpress.com/2017/04/heroin-in-co...