I didn't say "sudden". I think it would take time.
Addiction doesn't happen overnight. I am open minded and I am not going to ignore research if the research doesn't support my view. But my hunch is, it is too soon or too much damage has already been done and we need to take other steps to reduce usage not just legalization.
Incidentally I thought I saw some research that showed the opposite effect but I can't find the link right now... I'll take a look for it later and see if I can find it.
Hence I wouldn't really expect legalization of any drug X to improve problems with any drug Y in most cases. But if legalization itself helps with drug problems in general, I might expect that only legalizing drug Y would help drug Y's problems.
I suspect it will be about a decade before any really good analysis can be done on that aspect.
I don't think anyone (even the parent commentor) thinks that would happen. At best, I think we can only hope for prevention, and even that will require a lengthy period reeducation and destigmatization. Speaking from experience, it's nearly impossible to truly reverse opioid addiction. Preventing that addiction in the first place by utilizing other non-or-less-addictive pain control methods, such as marijuana, is our only hope.
As prescription opioid deaths drop 6 percent in Colorado, heroin deaths rise 23 percent
vs.
Overall, the total number of opiate deaths — meaning deaths from both prescription painkillers like fentanyl or from illegal opiates like heroin — fell by about 6 percent, from 472 deaths in 2015 to 442 deaths in 2016.
Well, Colorado tried that. Recreational weed has been fully legal in Colorado since January 1, 2014. You can walk down any major street in Denver or Boulder and pass multiple outlets selling marijuana. And they've sold lots of it, according to the tax receipts raised.
The result has not been the sudden reversal of opioid addiction that you had hoped for.
In 2015, opioid overdoses in Colorado continued to increase at the same rate as prior to legalization of marijuana. That year, opioid overdoses killed more Coloradans than homicide. [0]
In 2016, the total number of opioid deaths dropped 6%, but the number of heroin overdoses continued to increase. [1]
Personal experience in Portland Oregon suggests that in that city, legal marijuana has not made a dent in the meth and heroin issues that are still affecting the city.
Maybe recreational marijuana laws have helped. Nothing in this data can disprove that maybe more people would have died without it. But it hasn't been a magic bullet. It hasn't yet gone "a long way to" solving the problem of heroin overuse.
[FWIW, I'm in favor of recreational marijuana legalization, but the problems of heroin have different roots and we can't expect legal marijuana to immediately solve those issues.]
[0] http://www.denverpost.com/2017/01/03/colorado-opioid-heroin-...
[1] http://www.denverpost.com/2017/03/07/colorado-opioid-heroin-...