Using this item with your Improved Thief Blade or Serrated Thief Blade will add 1d6 Poison damage to an attack a target struck by a successful Stealth Attack.  It will also cause the target to be poisoned for 1 minute upon failing a DC 15 Constitution saving throw. 

Poison from this item can be applied to your Thief Blade as a Bonus Action.  The poison lasts for 1 minute before it must be applied again.  On a successful attack, the poison is used up and must be reapplied. 
A poison vial holds 3 chargers and must be refilled after 3 uses.  Any Poison can be used in the vial for this upgrade, however any secondary effects of the poison are lost.

Notes: The Poison Upgrade requires Poison in a Glass Vial, the type of poison does not matter so long as the Poison can be used by the Blade's delivery method. The Poison used retains it's normal effects.