This free and open source article discusses poly-substance use and opioids.
In my groups I worked with a handful of seniors with substance use disorder: opioids. Most were also dealing with pain management issues as well.
As a senior, addict (cannabis), and in chronic pain I could never quite grasp (then or now) or considered the idea/use of poly-substances. And it didn’t matter, not understanding the complexities of behaviors didn’t prevent me from providing care to all.

Fentanyl overdoses among seniors surge 9,000% — A hidden crisis few saw coming.
Fentanyl-stimulant overdoses is claiming the lives of older adults at unprecedented rates. Link below.

https://www.sciencedaily.com/releases/2025/10/251012054606.htm