De Materia Medica (Latin for "On Medical Material") is an encyclopaedia and pharmacopoeia of herbs and the medicines that can be obtained from them. The five-volume work describes many drugs known to be effective, including aconite, aloes, colocynth, colchicum, henbane, opium and squill. In all, about 600 plants are covered, along with some animals and mineral substances, and around 1000 medicines made from them.