Phencyclidine (a.k.a. angel dust or PCP) is particularly nasty.

Back in the early 1970s I was offered lines of what was supposed to be cocaine at a party I was hosting. Halfway through the first line I stopped abruptly and blew out my nose as soon as I realized what was happening. Too late.

I yelled, "I've been poisoned" and in a panic ran down to the basement and hid behind the furnace. My girlfriend was at work and not due home for a couple more hours. After who knows how long, the PCP started to wear off and I started to get off on the LSD it was  mixed with. That changed everything. The LSD high was like coming back to a safe home after the PCP nightmare. I came back upstairs and enjoyed the rest of the night with a mild (probably <50mcg) acid buzz.

Lesson learned. Don't go snorting long lines just because someone else says it's what he thinks it is. Do a tiny tester first. Thank gawd they hadn't invented fentanyl yet.