…Amongst its multitude of uses, Warpstone can be administered
as a drug. It is most commonly powdered and used as a snuff. Aside from a giddy feeling of self-confidence, Warpstone dust increases the magical abilities of any Skaven that ingests it. Prolonged use of Warpstone causes mutations in addicts, and these deformities are viewed by other Skaven with a combination of awe and contempt. Warpstone snuff is expensive and rare, so it is rarely seen in the possession of Clanrats; it is generally held by Grey Seers, Chieftains, and Warlords, among a few others…

- Children of the horned rat, Chapter III, page 41