Perhaps the deadliest manufactured poison is Formula 3T-9, better known today as Thasmudyans Bile. This terrible poison was created by the Lith-Crillion working out of the Pyramid of Alchemy. Formula 3T-9 was re-discovered in the Second Epoch by explorers serving the Cult of Worms.
Thasmudyans Bile has a Fortitude DC26, initially causes 1d10 constitution damage and 1-4 charisma damage followed by 1d12 constitution damage and 1d2 charisma damage on the second round. There is a 10% chance for each charisma point lost to be permanent; recoverable only by use of spells like Wish.