It's a mystery.
https://en.wikipedia.org/wiki/Speedball_(drug)
That'll get you started.
Another related problem is the narrow therapeutic range of legal and illegal opioids combined with inadequate prescription duplication and overlap detection leads to less aware patients taking multiple substances and/or taking too much leading to unintentional OD.
Cpoll•3mo ago
> 2015 and 2023, fentanyl-related deaths rose from 264 to 4,144 among older adults (a 1,470% increase) and from 8,513 to 64,694 among younger adults (a 660% increase). Within the older population, deaths involving both fentanyl and stimulants grew from 8.7% (23 of 264 fentanyl deaths) in 2015 to 49.9% (2,070 of 4,144) in 2023 -- a staggering 9,000% rise. In comparison, among younger adults, fentanyl-stimulant deaths rose from 21.3% (1,812 of 8,513) to 59.3% (38,333 of 64,694) over the same period, a 2,115% increase.
And without stats for other types of ODs and for population size to compare against, it's hard to draw conclusions. Not to say that I dont't there's an opioid epidemic.
saulpw•3mo ago