Gadwall helps a witcher's mutated body regenerate much faster than usual. No wonder witchers often consume it when preparing to fight especially powerful beasts. Gadwall is a stronger version of the Swallow potion. As Gadwall courses through the veins, however, it burdens a witcher's body, causing him to deal less damage and lose Vigor at an accelerated rate. These side effects can be reduced by drinking the Rook and Tawny Owl potions.
Potion significantly increases Toxicity when imbibed.
Gadwall is recommended before long fights. Its slow but constant regeneration of Vitality provides its user with an advantage over opponents..