In an earlier post, I wrote that about 20-25% of drug poisoning deaths involved some kind of chronic health condition. See what I wrote. I think this calls into question whether these were truly drug overdoses. If a death certificate for a supposed opioid poisoning has “sleep apnea” and “obesity” listed on it, that calls into question whether, in a “but for” sense, the death was caused by the drugs. It's more accurate to say that the death was a combination of a drug overdose (drug interaction, in most cases) and a pre-existing health condition.
I’ve done some more thorough analysis, and it looks like I was on the right track with the 20-25% figure. I can’t give any details just now, but I’m glad I stumbled on this path. Will share details and acknowledgements when I can.
I also know quite a lot more about how the death certificate is filled out, how the causes of death get coded in the ICD-10 codes, how an “underlying cause” is selected from the various causes listed on the certificate, how the different parts of the certificate work, etc. When I wrote that post (linked above) a couple of years ago, I had no idea about any of this. I guess I just assumed it was a bunch of contributing causes listed in no particular order. The story is a little more complicated than that. I may have to do a “death certificate explainer” post when the paper I’m working on comes out. I don’t think the stuff I know now invalidates anything I wrote before, but the details are interesting.