Take this with a grain of salt because im not a scientist and this is just conjecture but Im fairly certain dogs can smell the chemistry of drugs in your system but they have no concept of "drug" so they would likely know but not know if that makes sense

My dog knew if I was high cause I smelled weird and acted kinda weird but he had no idea what any of that meant so he would just stare at me--that said I was doing a lot of acid that summer and maybe him staring at me "weird" was just me being on acid...

Dogs are 4 legged mass spectrometers. They can tell if anything is wrong with your metabolism and they can tell when you have dope in your system. It upsets them because it is unfamiliar.

Oh great! I already stress out thinking that every human knows I'm high, now I need to be paranoid about my dog knowing I'm high too?!?

I had a dog that could tell when I was stoned and then would put his paw on my arm until I blew a hit in his face. Then he'd lay down and watch cartoons with me.

Can dogs tell when I need hugs?

My dog could tell when I was on some ketamine for the first (and likely last lol) time