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Botanical name: Quercus spp.


© Steven Foster

Parts used and where grown

Oak trees grow throughout North America. Some species of oak grow around the world, including in China and the Middle East. The bark of the oak tree is used medicinally.

Oak has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings Health Concerns

Canker sores

Crohn’s disease




3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Historical or traditional use (may or may not be supported by scientific studies)

Oak bark was used traditionally by herbalists to treat hemorrhoids, varicose veins, diarrhea, and cancer. Tannic acid derived from oak trees has a long history of application in tanning hides and making ink.1

Active constituents

Tannins are the primary constituents of oak bark.2 These tannins are potent astringents, akin to those found in witch hazel (Hamamelis virginiana). Tannins bind liquids, absorb toxins, and soothe inflamed tissues. The oak tannin, known as ellagitannin, inhibits intestinal secretion,3 which helps resolve diarrhea. The nonirritating, astringent nature of oak has led to its recommendation for treating mild, acute diarrhea in children (along with plenty of electrolyte-containing fluids) in Europe.4 Astringents such as oak may also help relieve the pain of sore throats and canker sores.

How much is usually taken?

The German Commission E monograph suggests 3/4 teaspoon (3 grams) of the bark per day.5 For eczema, oak is applied topically by first boiling 1–2 tablespoons (15–30 grams) of the bark for fifteen minutes in 2 cups (500 ml) of water. After cooling, a cloth is dipped into the liquid and applied directly to the rash several times per day. The liquid prepared this way in the morning can be used throughout the day. Unused portions should then be discarded. Up to 5 cups (1250 ml) of this same solution can be taken each day in cases of diarrhea. Alternatively, a tincture of oak, approximately 1/2 teaspoon (2–3 ml) three times daily, can be used.

Are there any side effects or interactions?

Except for the occasional upset stomach or constipation reported after drinking the tea, oak bark is rarely associated with side effects. There are no known reasons to avoid oak during pregnancy or breast-feeding, though oak can cause constipation. It is safe for use in children and infants. The German Commission E monograph warns against people with open sores, wounds, high fever, orinfection bathing in water with oak bark.6

Are there any drug interactions?
Certain medicines may interact with oak. Refer to drug interactions for a list of those medicines.


1. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Foods, Drugs, and Cosmetics, 2d ed. New York: John Wiley & Sons, 1996, 485–7.

2. Weiss RF. Herbal Medicine. Beaconsfield, UK: Beaconsfield Publishers Ltd., 1988, 328–9.

3. Konig M, Scholz E, Hartmann R, et al. Ellagitannins and complex tannins from Quercus petraea bark. J Nat Prod 1994;57:1411–5.

4. Schilcher H. Phytotherapy in Paediatrics. Stuttgart, Germany: Medpharm Scientific Publishers, 1997, 49–50.

5. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 175–6.

6. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 175–6.

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