Dusk Leaf

Dusk Leaf is a type of narcotic plant found on the Death World of Yanth. Though appearing as little more than a dark purple weed, it is part of a sector-wide smuggling trade. When dried and ground, the resulting substance can be smoked or injected in a careful ritual, giving an unearthly, sensory-expanding experience that is a part of several cult rituals.

The drug is addictive, with each dose causing unnatural, sensory input between one to five solar hours. Perhaps worst of all, if not taken with proper knowledge for applying Yanthian drugs, a given user risks any number of other hallucinatory effects.

Source

 * Dark Heresy (2nd Edition): Enemies Without (RPG), pg. 101