I met a person who, while on a ~1/2 lb dose of psylocybin mushrooms, fell face first down stairs onto a train platform without even putting his hands out, breaking his nose, smashing out all his front teeth, and getting a severe concussion--it's easy to see how this could have been much worse had he fallen off the train platform.
And that's just the physical effects. I've met a few people who were fingerprinted (moisten a finger, press it into a tray of crystalline LSD, and consume whatever sticks to your finger) and at those doses, they all reported long-term hallucinations (in medical parlance, hallucinatory persisting perception disorder or HPPD). Others were diagnosed with PTSD after bad trips (one reported being "psychically attacked" by evil spirits, another was convinced that everyone was trying to kill him).
There are numerous cases of people being assaulted sexually or violently while on hallucinogens, and feeling that they could have defended themselves had they not been tripping. That's not to say they are to blame for the actions of their attackers. People who are on drugs are vulnerable, but the reaction I'd like to see is not to blame them, but instead for communities to care for them and protect them while they're vulnerable.
Now, I'm well aware that as someone volunteering in harm reduction, I only got to see the bad cases. For every patient reporting a negative experience, there are hundreds if not thousands of people who use hallucinogens and have positive experiences. I'm not against drug use, I'm merely advocating that people do so in an educated, responsible manner, understanding the very real risks they're taking. Just because the LD50s of LSD and psilocybin are very high, doesn't mean that a high dose of these drugs is not risky.
This document (PDF) from the Multidisciplinary Association for Psychedelic Studies (MAPS) claims:
The LD50 of LSD varies from species to species. The most sensitive species is the rabbit, with an LD50 of 0.3 mg/kg i.v. [52]. The LD50 for rats (16.5 mg/kg i.v.) is much higher [52,53], though mice tolerate doses of 46– 60 mg/kg i.v. [52,54]. These animals expired by paralysis and respiratory failure. Monkeys (Macaca mulatta) have been injected with doses as high as 1 mg/kg i.v. without any lasting somatic effects [55].
There have been no documented human deaths from an LSD overdose. Eight individuals who accidentally con- sumed a very high dose of LSD intranasally (mistaking it for cocaine) had plasma levels of 1000–7000 μg per 100 mL blood plasma and suffered from comatose states, hy- perthermia, vomiting, light gastric bleeding, and respira- tory problems. However, all survived with hospital treat- ment and without residual effects.
https://maps.org/research-archive/w3pb/2008/2008_Passie_2306...