Let's not go black and white here. Mentally and physically healthy people will probably never suffer adverse effects from LSD or any other similar psychedelic, as long as they are responsible users.
However, there are endless accounts of people who become psychotic and delusional on small doses of far milder drugs, so saying that a power horse like LSD is completely safe is very, very misleading.
As we all know, metal illnesses are often inactive until life events make them surface. Generally speaking, single uses of LSD carry very little inherent risk even for people with preschizophrenia symptoms, but it's certainly still there.
