pharmacognosy

n. study of the characteristics and uses of drugs

Pharmacognosy is the study of medicines from natural sources. The American Society of Pharmacognosy defines pharmacognosy as "the 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 the search for new drugs from natural sources".
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Pharmacognosy /phar·ma·cog·no·sy/ the branch of pharmacology dealing with natural drugs and their constituents. phar·ma·cog·no·sy n. [more]Pharmacognosy - Community and Resources

(n.)
Pharmacognosis.
  

The pharmacology subfield whose focus is medically useful substances that occur naturally, primarily those synthesized by medicinal and other plants.