I guess my angle is that of someone who only really eats opiates most of the time... you can feel the OD coming a mile away. Especially if it's opium. You know if that 2nd hour is strong, then the 3rd might be dangerous. Those building waves are quite predictable with a good opium.
If I'm honest. I've never really been to the edge, or maybe I have but I was too naive and I just remember it as sleeping well or something, hard to tell sometimes. I'm not exactly hardcore or with a high tolerence, but I have played a lot (not sure if I should undersell of oversell my experience here). I have "OD'd" on kratom a lot, you just nausea. The point being if that is an analogy for a real OD, I felt it coming before it hit it's peak of worse-ness.
So maybe, it could work with slowly metabolised oral opiate situations? That is my interest, because I will not be IV'ing or smoking massive hits that KO me in one go. At least I hope I won't be ever. But it's nice to ingest something with a reassurance that just in case you potentiated it too well, you might have recourse...
and, I should add (sorry for waffling, I forgot this wasn't even my thread) - I discovered that coffee works well in this capacity. There is various evidence and research into coffee, in particular instant coffee, being full of opiate antagonists. I have seen this twice in the last 2 days. It was very powerful pulling me out of quite a deep respiratory depressive buzz on opium back to almost just half a buzz, completely ruined my buzz tbh.
cheers