LSD's only known fatal toxicity in mammals has been in elephants; it causes heat regulation problems, and therefore might also be dangerous to other very large mammals. (It's probably a bad idea for aquatic mammals, in case disorientation can lead to drowning, but it can also be dangerous for human subjects that need to operate large machinery, such as cars.)
Damage to receptor molecules isn't much of an issue with LSD; that seems to be more of a risk with Ecstasy and the various dopamine-affecting drugs. Unfortunately, the DEA's bans on research make it really hard to study those effects on the recreationally interesting ones, compared to the more politically correct drugs. But for LSD, doses are really low and they only affect a few receptors, unlike some of the more complex psychedelics. On the other hand, for people who have risks for psychosis, it can be a really powerful and disorienting experience which they can't handle well.
I've stayed away from the serotonin-regulating drugs, but tried a dopamine-agonist for restless leg syndrome, and after using that for a few months and getting a bad reaction to nitrous at the dentist, it took me a couple of months to feel like myself again. Not planning to touch that stuff or anything like it again.