LSD is not unique in being of that sort of potency. There are several other related ergoloids that are of similar potency (though usually a bit less).
Some of the psychedelic amphetamines fall into this category too. Many have doses in the sub-1mg range. Some exotics (Bromo-dragonfly) are not only effective in the same dose range as LSD, but last several times as long and are far more toxic. The LD50 of LSD is quite forgiving as I understand it, with BDF it is not and people have died.
There are other substances that border on poison - carfentanil is an opiate used to stun elephants and is active in humans at the 1ug range.
I also dislike the catch-all term 'drugs', but LSD is not entirely unique in its potency.
Some of the psychedelic amphetamines fall into this category too. Many have doses in the sub-1mg range. Some exotics (Bromo-dragonfly) are not only effective in the same dose range as LSD, but last several times as long and are far more toxic. The LD50 of LSD is quite forgiving as I understand it, with BDF it is not and people have died.
There are other substances that border on poison - carfentanil is an opiate used to stun elephants and is active in humans at the 1ug range.
I also dislike the catch-all term 'drugs', but LSD is not entirely unique in its potency.