Once again, the number of deaths from prescription opiates is dwarfed by the number of opiate deaths from illegal opiates. There's not even a comparison. And the vast majority of the opiate deaths from illegal substances are from fentanyl and related substances, which are notoriously hard to dose and/or frequently spiked and/or passed off as drugs of lesser potency. Imagine the deaths we could prevent if we (as in Europe) allowed addicts to dose themselves with supervised, clean, hygienic, pharmaceutical-grade heroin while offering them treatment to get off of them if they so desired.
Edit: I looked up current data and it looks like prescription opiates like oxycontin account for about 1/3 of opiates deaths. Maybe not quite "dwarfed" like I claimed above, but a definite minority of opiate deaths are caused by prescription narcotics. And given the current growth rate of deaths from illegal opiates, it could easily be only 10% in the next 1-2 years: https://www.cdc.gov/drugoverdose/epidemic/index.html