"White Honey strongly stimulates the production of purifying enzymes in witchers' mutated bodies. Thus, it frees their bodies of the effects of toxicity, though it simultaneously nullifies the beneficial effects of any potions previously consumed. White Honey does not alleviate the effects of common venoms and poisons."
White Honey reduces Toxicity to zero and cancels the effects of other potions.
White honey is useful in situations where you don't have readily access to a fire, but urgently need to drink more potions - typically in-between intense combat. However, since it also removes existing potions effects, it is best used together with short-duration or instant effect potions, such as Blizzard or White Raffard's Decoction.
Geralt has the ability to brew this potion from the moment he arrives in White Orchard. Only one of the basic potions can be crafted at any one time and placed in the consumables slot, however this increases with each of the higher level veriants.