A truth potion, also known as a truth serum, is a potion created and used primarily by witches to force the drinker to tell the truth. It is often used to extract information that the drinker would not give up under normal circumstances, and so is useful in interrogations. The exact ingredients and process of making the potion are unknown, though it is mentioned that calamus and bloodwort are used in the potion. Some people have severe allergic reactions to the serum, which renders them extremely weak and near comatose. Unless treated using strong medicine (usually prepared and administered by a trained healer), the effects could prove fatal.
In Black Dawn, Sylvia Weald attempted to use a truth potion on Aradia Crowley to extract information on Circle Daybreak; however, Aradia had a reaction to the serum, which nearly killed her. Sylvia was unable to obtain anything useful from her and the Maiden eventually recovered after being treated by a healer.