D&D 5.5e Dungeon Master's Guide
Poison
Varies
A creature who ingests Assassin's Blood makes a DC 10 Constitution Saving Throw. On a failed save, the creature takes 6 (1d12) Poison Damage and has the Poisoned Condition for 24 hours. On a successful save, the creature takes half damage and is not poisoned.
Assassin's blood is a clear, odorless fluid with a slightly metallic taste, that has been used for hundreds of years in the schemes and machinations of mortals. It's not especially deadly, but sneaking it into the food of an unsuspecting target has a plethora of uses other then assassination.
Cost: 150 gp
Weight: .3 lbs