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…