Not to mention acetaminophen/paracetamol. Alcohol is something like 10:1, tylenol may be as low as 3:1. Morphine is much safer, 70:1 or so - not sure about heroin.
I do think inconsistent supply is a larger contribution to OD risk than the relatively tight TI, but this is hard to study properly partially because of criminalization.
I was going off this table: https://web.cgu.edu/faculty/gabler/toxicity%20Addiction%20of... (page 689), which does not include morphine. it's surprising that the margin is so much larger for morphine, since heroin is essentially a prodrug for morphine. the figures I found for morphine all seem to assume an oral ROA for morphine, but IV for heroin. perhaps that explains some of the difference? it could also be that the definition of "effective dose" is different in an abuse context vs. a medical one. also now that I go back and look more closely, it seems the TI of opioids is a fairly wide range, so my comment is not entirely correct as written.
I'm glad you brought up paracetamol as well. I find that people often overestimate how dangerous illicit drugs are, while at the same time being totally blase when it comes to stuff you can buy off the shelf at any pharmacy. frankly, I find tylenol kind of scary and try to use it only when absolutely necessary.
Except of course it's pretty difficult to consume 10x the amount of alcohol without puking, and people develop tolerance to morphine, which shrinks the safety margin, and makes it dangerous if a formerly "normal" dose is injected after a relapse.
I do think inconsistent supply is a larger contribution to OD risk than the relatively tight TI, but this is hard to study properly partially because of criminalization.