Yarrock was an addictive spice and a strong hallucinogen. Originally synthesized by Iridonian shamans as a preparatory aid given to warriors before battle, yarrock was said to instill a person with a clear vision of "the meaning of life", to either kill or be killed, thereby boosting their confidence temporarily. Constant use of the spice lead to the side effect of psychosis. For transport away from Iridonia, yarrock was preserved in tiny black plastene packets to maintain its potency and to prevent moldering due to its sensitivity to moisture. Drub McKumb was a user of yarrock.