Quoting so it's easier to see for me as I write.

i do way too much street fent, nearly die, and wake up in an alley somewhere, am i responsible for what happened to me in between those points? Or not? It's not like i stopped existing as a person. Physically, i am fully responsible for what happened in that state, psychologically, i am to some degree at the very least tangentially responsible. (there is a reason why you cant drink and drive)

In terms of consent based events, no. If someone else takes advantage of your state, even the voluntary intake of substances doesn't remove the obligation to obtain meaningful consent from the inebriated person by any other party.

It also depends on the substance. Some stuff, you have way less ability to function consciously. Others, you're changed so little as to be kinda irrelevant outside of determining the exact consequences in a complicated situation. As an example, if someone slams too much caffeine and punches somebody, that's 100% on them in any normal circumstances. Something like weed, you run into edge cases where it might be a mitigation, but not as much since there's less inhibition of the conscious mind compared to something like fentanyl. A pothead robs a store with their buddy, I'm not going to believe they couldn't have refused because of the weed (under normal circumstances). If they're barely functional from opiates, I might buy that they didn't really know what was going on, and got swept up in things.

That last one is a real thing I've run across a few times. Dudes thieving while high and claiming to only have been dragged along, and then having something shoved in their hands and be told to run. It's believable with some drugs, less so with others.

Like anything about human behavior and social rules, the more specific things get, the easier it is to throw down a definite yes/no regarding culpability. The more general it stays, the more you have to deal in a degree of "usually, but".

That is separate (in my opinion as well as in law in some places) from the inebriated person committing bad or illegal acts themselves.

There's also a middle ground where a person that's inebriated may have some degree of exculpatory claim if someone used their altered state to get them to commit a bad or illegal act. They'd still be responsible, but any judgements on their acts should take it into account (socially and legally).

Edit: also, I apologize for taking so long to respond, but I was having trouble reading for some reason, and I couldn't use tts when I first got the notification. Dyslexia is fucking weird sometimes. I don't usually have this much trouble lol.