(also phlorhizin, phloridzin, phlorrhizin), an organic compound belonging to the glycoside group; the O-glyco-side of phloroglucinol (1,3,5-trihydroxy-benzene) combined with a residue of phloretinic (β-parahydroxy-phenylpropionic) acid. Phlorizin is found in the roots, stems, and baric of plum, cherry, pear, and apple trees. It is used in biochemical and physiological research.

When injected into animals, phlorizin blocks the reverse absorption (reabsorption) of glucose into the blood from the renal tubules. As a result, glucose is discharged with urine (glycosuria) even though its level in the blood is not abnormally high. Experiments with phlorizin have made it possible to establish that an unvarying level of glucose in the blood is maintained initially by the breakdown of glycogen; subsequently, gluconeogenesis occurs, that is, the formation of glucose from noncarbohydrate precursors—intermediates of the tricarboxylic acid cycle. Phlorizin also inhibits photophosphorylation in chloroplasts and phosphorylation in mitochondria.