The term comes from two Greek words: "pharmakon" meaning drug or medicine, and "gnosis" means knowledge. The American Society of Pharmacognosy explains pharmacognosy as "the branch in which we study of the physical, chemical, biochemical and biological properties of drugs, drug substances or potential drugs or drug substances of natural origin as well as focus is laid on search for new drugs from natural sources". Plant based preparations are said to be medically beneficial in a condition when they are used to promote health above the basic nutritional requirement. The knowledge of drugs from herbs includes the subjects of chemistry, botany and pharmacology. Botany includes the identification (taxonomy), genetics, and cultivation of plants. Chemical characterization of these drugs includes the isolation, identification and quantification of active phyto-constituents from plant materials. In this, we study of the biological effects that the chemicals in medicinal plants exert on cell cultures, animals and humans.