Why is Botulinum toxin the most potent poison known? Botulinum toxin (trade name Botox) inhibits acetylcholine release in neurons and causes botulism, an acute paralytic disease which leads to nerve degeneration and takes a long time to recover. I've read the statement that Botox is the most potent poison we know a few times now and was wondering _why exactly_ it is. All sources I've found only claim _that_ it is, without explanation.

A quick search for a list of LD50 (median lethal dose; half of the people will die with that dosage) gave me 1 ng/kg for Botulinum toxin. This is pretty darn small amount, and in fact the smallest amount within that table.