Even knowingly ingesting hallucinogens can be not fun.

I unknowingly smoked some opium laced pot with some strangers at a party once. They were already pretty wasted so it did not occur to them to warn me until after I was already smoking. It mostly led to a rather dreamlike night of revelry so no complaints about that one.

I shared a blunt with a stranger and pretty sure it had PCP in it. I was stuck in a chair for at least an hour.