Laq was a pernicious drug that caused an altered state of mind. Excessive use caused raving, uncontrollable battle-rage, and an enraged laq user could sustain mortal wounds and continue to fight. Laq-users displayed a blackened tongue as a consequence of use. Rumor held that laq was created as an elixir by the nobility to increase the endurance of slaves, but its side-effect of inducing rage (and the same side-effect as a result of withdrawal) made it unsuitable for that purpose.
Sources[]
The Brazen Gambit (July 1994), (ISBN 1-56076-872-X)