Most of all, in medicine, oak bark is valued and used, especially young and shiny, due to the presence in it of a large amount of tannin - catechin, other substances are less valuable. It is used more as an external agent, as well as for douching, enemas, less internally, in the form of infusions, decoctions, tea. The bark and leaves of common oak have astringent, anti-inflammatory, antihelminthic, soothing, hemostatic effects. The infusion is taken for diseases of the stomach, diarrhea, gastritis, colic, inflammation of the intestines, colitis, ulcerative colitis, gastrointestinal bleeding, liver disease, spleen. Warm infusion improves digestion.