# Oak bark *Tanner’s bark; the bark of the common or English oak, *Quercus robur* of Linnaeus, which the European monograph takes together with the sessile oak, *Quercus petraea*, and the downy oak, *Quercus pubescens*; in pharmacy *Quercus cortex*; the Greek *drus* of Dioscorides* **Known today as.** The bark of the common oak, collected in spring from young trees, dried in the sun, greyish and somewhat polished outside and brown within. Grieve describes it as “slightly tonic, strongly astringent and antiseptic,” with a strong astringent bitter taste and a slightly aromatic smell. The galls of the oak have an entry of their own, [Oak galls](https://thethinkingpress.org/materia-medica/oak-galls). Kind: Plant > **Caution.** Because it can slow the absorption of medicines taken at the same time, the European agency advises taking it at least an hour before or after other medicines. Not for anyone under eighteen, for want of data. As a bath it is not for open wounds, large injuries to skin or mucosa, or infections of them, and hot baths are not for fever, infection, heart failure, or high blood pressure. Recurrent diarrhoea, bloody stools, or rectal bleeding call for a doctor. Allergic reactions have been reported. ## What was it used for? The astringent of the hedgerow, given for diarrhoea, dysentery, and bleeding. Grieve has the decoction taken in wineglassful doses in chronic diarrhoea and dysentery, used as a gargle in chronic sore throat with a relaxed uvula, and applied to bleeding gums and piles; she reports it once given as a substitute for quinine in intermittent fever, and powdered and inhaled in early consumption, “Working tanners” being, she says, well known to be particularly exempt from that disease. The bark tanned leather everywhere, and dyed wool purplish with copperas and black with iron. ## What does modern science say? The European Medicines Agency’s herbal committee accepts oak bark as a traditional herbal medicine, “exclusively based upon long-standing use,” for the symptomatic treatment of mild diarrhoea, of minor inflammation of the mouth or the skin, and of the itching and burning of haemorrhoids once a doctor has excluded anything serious (monograph of 2010). Its assessment report puts the bark’s tannins at a highly variable 8 to 20 per cent, both the hydrolysable kind that yield gallic and ellagic acid and the condensed kind, the amount depending on the time of harvest, the age of the branches, and the method of assay. ## Pharmacognosy and toxicology - **tannins**: 8 to 20 per cent, both hydrolysable and condensed - **gallic**: yielded, with ellagic acid, by the hydrolysable tannins - **ellagic acid**: **Mechanism.** An astringent: Grieve calls the bark “strongly astringent”; the European agency notes it can slow the absorption of other medicines taken with it. **Standing.** European Union herbal monograph (2010): traditional use, “exclusively based upon long-standing use,” for mild diarrhoea, minor inflammation of the mouth or skin, and haemorrhoids. ## What lore surrounds it? “The Greeks held the Oak sacred, the Romans dedicated it to Jupiter, and the Druids venerated it.” In England, Grieve writes, Gospel Oaks marked the parish bounds, where the clergy stopped to read the Gospels in the yearly procession; the country proverb set the leafing of oak against ash to forecast the rain; and in South Wiltshire villagers wore oak on the 29th of May and claimed their right to fallen wood with the shout of ‘Grovely, Grovely, and all Grovely!’ She records the great trees, the Fairlop Oak of Hainault Forest at 36 feet round, the Newland Oak of Gloucestershire at 46, and reports that Philip of Spain ordered the Armada to burn every oak in the Forest of Dean. A superstition held that whoever cut or maimed Abraham’s Oak at Mamre would lose his firstborn son. ## What did the older authorities say? **Dioscorides.** Every part of the oak is astringent, he says, but the film between bark and wood, like the skin under the acorn’s cup, is the best for the bowels: boiled and drunk for dysentery and for spitting of blood, and pounded into pessaries for excessive discharges of the womb. Acorns are diuretic, and a decoction of them and the bark in cows’ milk helps against poison. **Nicholas Culpeper.** “Jupiter owns the tree.” The leaves, the bark, and the acorn cups “do bind and dry very much,” and the inner bark and the thin skin of the acorn stay spitting of blood and the bloody flux. Hippocrates, he writes, used the fumes of oak leaves on women troubled with the strangling of the mother, “and Galen applied them, being bruised, to cure green wounds.” The water found in the hollows of old oaks is “very effectual against any foul or spreading scabs.” ## Sources - Grieve, M. *A Modern Herbal*, “Oak, Common.” As published on botanical.com. - Culpeper, N. *The Complete Herbal*, “The Oak.” Project Gutenberg, 49513. - Dioscorides. *De materia medica*, 1-142 and 1-143, in the modern English version of T. A. Osbaldeston and R. P. A. Wood (Johannesburg: Ibidis, 2000), after Goodyer’s translation of 1655. Internet Archive. - European Medicines Agency, Committee on Herbal Medicinal Products. *European Union herbal monograph on Quercus cortex (Oak Bark)*. EMA/HMPC/3203/2009, 25 November 2010. - European Medicines Agency, Committee on Herbal Medicinal Products. *Assessment report on Quercus cortex*. EMA/HMPC/3206/2009, 25 November 2010. - European Medicines Agency, Committee on Herbal Medicinal Products. *European Union herbal monograph on Quercus cortex (Oak Bark)*. EMA/HMPC/3203/2009, 25 November 2010. - European Medicines Agency, Committee on Herbal Medicinal Products. *Assessment report on Quercus cortex*. EMA/HMPC/3206/2009, 25 November 2010. - Grieve, M. *A Modern Herbal*, “Oak, Common.” As published on botanical.com. --- *Oak bark.* In *Materia Medica*, edited by B. C. P. Statema. Version 1, revised 2026-10-16. The Thinking Press. https://thethinkingpress.org/materia-medica/oak-bark Historical description, not medical advice.