Saigenzai (催幻剤, literally meaning: Hypnotic Illusionary Medicine) is a type of drug that produces genjutsu, mentioned in Naruto Jinraiden: The Day the Wolf Howled. Because the genjutsu is administered through a drug, it does not rely on a user to keep it in effect and it's able to have a stronger hold on those who it's used on. Depending on how it's prepared, saigenzai can create "malfunctions" in a person's vision, hearing, and semicircular canals. Members of the Kodon clan are able to prepare a special version of saigenzai called Kotarō, which can be used to treat severe illnesses.
Saigenzai is popular in the Howling Wolf Village as a narcotic, used by former shinobi to cope with their uneventful and/or traumatic lives. Frequent users are identifiable by their dark eyes and pale complexion; Sasuke Uchiha, because he always looks like that, is initially mistaken for such a user. These former shinobi variously call saigenzai "the pill of ascent", "the powder of heaven", "the pill of affection", and "the pill of perturbation". Because saigenzai can be deadly to those who take it improperly, it is illegal within the village.