Crude drugs are naturally occurring substances derived from plants, animals, or minerals that are used to treat diseases. They can be organized, with cellular structures from plant sources like fruits and roots, or unorganized substances obtained indirectly through extraction or distillation like oils and gums. Crude drugs are classified in several ways, including alphabetically by name, taxonomically by biological classification, morphologically by physical structure, pharmacologically by therapeutic use, chemically by important constituents, and by chemical or antigen-antibody similarity within taxonomic groups. The classification system provides information on a drug's source, constituents, and relationships to other species.