The estimated average lethal dose for LSD in humans is only 100 mg, based on rodent studies. Far less than caffeine and even amphetamines.

LSD does cause significant psychoactive effects with one thousandth of that amount, which suggests that for a typical isolated dose, LSD is safer than caffeine and amphetamines. Not to mention that LSD is not as addictive.

But I don't think that invalidates my underlying point regarding caffeine, even if the lethal dose is not a perfect measure.