If I were a public health official, I think my number one question right now would be whether increased marijuana usage- and legalization- is going to contribute to the opioid epidemic or help slow it down. Is smoking weed a substitute for opiates or a complement?
Looking at the state maps of marijuana usage (from SAMHSA) and overdose deaths (from CDC Wonder) , you can make arguments either way. The Northeast has had a shockwave of opioid deaths, along with high and climbing rates of marijuana usage. On the other hand, the West Coast states (along with Colorado) which have had the broadest legal usage have had relatively slow increases in opioid deaths.
This might all just be spurious, but you could tell a story here where buying marijuana illegally from a dealer (and dealers developing customer relationships and supply routes) contributes to buying opiates illegally later as well, but using marijuana legally (either for medical reasons or recreationally) is a substitute for opiates. At least two papers suggest that medical usage of cannabis is associated with lower opioid usage and lower overdose rates.
If this is right, I would hope to see Maine and Massachusetts- both of which had explosive rises in opioid deaths through 2015 and whose voters approved recreational marijuana in November 2016- slow down their overdose rates in 2017, which would be very good news. I don’t have a particular fondness for pot as a drug, and I thought it was moderately bad news for many of the kids I grew up with, who started smoking a ton in high school. The small number of my former students I know of who developed opiate issues also smoked a lot of weed in high school. But I’m willing to be convinced that the benefits of legalization will outweigh the risks.