If that were the case then there would be a decline in heroin use in Washington State which has legalized marijuana. Heroin is booming in the PAC NW. The vast majority of it originates in Mexico. Despite what many people think, the booming Afghan opiate product goes other places than the US.
You are making a false comparison. The article deals with the reduction of death from prescribed opioids when legal marijuana can be prescribed for pain relief. It makes no claims regarding deaths from the use of illegal drugs such as heroin.
I don’t see how they could reach a firm conclusion since marijuana has been legal for such a short time. I can’t access the study but I would hope they would address efforts those states have made to reduce opioid deaths such as trying to reduce pill mills.
I do stand corrected. One part of the abstract mentions just deaths from prescribed opioids the other mentions deaths from both legal and illegal use. I would not expect see a reduction in deaths from illegal drugs cause I sincerely doubt most are under the care of a physician or using heroin to treat chronic pain. Most likely medical marijuana would not be considered a viable alternative to them.
What does illegal heroin have to do with the pharmaceutical industry? Furthermore, heroin use has been on the rise for at least a decade, even while marijuana was illegal.