Boosts your attack power by filling you with - guess what? - demonic strength.
Demondrug can be consumed from the Item Bar while in the field to increase Raw (Physical) Attack Power by 5. This boost lasts until carting or Quest completion, and This buff stacks with boosts to Attack Power from Hunting Horn melodies, Canteen meals, and other consumables - with the exception of Mega Demondrug, which will replace it.
Demondrug is used to craft said Mega Demondrug - a direct upgrade - and Demon Ammo, which can be used to apply the effect to Allies.
How to Acquire Demondrug
Demondrug is obtained through Crafting and can be used to create the more powerful Mega Demondrug or Demon Ammo.