Rot

Uncommon illicit substance
This black, tar-like liquid is harvested from undead creatures by unscrupulous necromancers and dark priests. Essentially distilled blood of an undead creature, Rot smells bad and tastes worse.
The dark liquid, which is sold in small vials, carry traces of the necromantic energy that fuels the undead, allowing anyone to gain a brief taste of an undead creature's numbed existence.
Despite it's foul nature, Rot is very popular among street beggars and vagrants, who use it to keep pain and hunger at bay.
Rot-users are easily recognizable by their grayish skin, dead eyes and often ghastly smiles. Long-time users also show signs of hair loss, decaying teeth and general muscle atrophy.
Rot is also known as 'ghoul's blood' or 'grave drink'. Users often refer to the consumption of rot as 'rotting' or 'gravecrawling'.
Dose. An ounce of dark liquid. A single dose of Rot costs around 25 gp, while a small flask containing ten doses sells for 200gp
Use, drinking Rot is a standard action
Effect. Immediately after consuming a dose of Rot, you begin to feel numbed in both mind and spirit. For 8 hours, you have a +4 bonus to your Constitution score and you don't need to breathe, sleep, drink or eat. You also have disadvantage on Dexterity saving throws and ability checks.