Educational information, not medical advice — ask your doctor or midwife.
Cashew bark is the bark of the cashew tree, Anacardium occidentale. In Yoruba the tree is called kaju. Healers boiled the bark in water to make a bitter brown wash or drink.
It is not the nut. The nut is a food, sold everywhere. The bark is a folk remedy, used for loose stools, sore mouths, toothache and "sugar sickness".
Here is the honest verdict. Human evidence for cashew bark is very thin. Almost everything known comes from test tubes and animals, and long use in tradition is not proof that it works or that it is safe.
No one has shown how cashew bark works in people. The ideas below come from lab and animal work only.
The bark is rich in tannins. Tannins are astringent, meaning they bind proteins and pucker tissue. In lab work this can firm up gut lining and slow fluid loss, which may be why the old use was for diarrhoea.
In test tubes, bark and leaf extracts slow the growth of some bacteria and yeasts. Whether that happens inside a person is not established.
In rats, stem bark extracts have lowered blood sugar. The doses and the animals are not the same as a cup of bark tea. No trial has tested this in people with diabetes.
The bark also holds anacardic acids. In cell studies these block certain enzymes. The same compounds can burn skin, so a lab effect here is not good news on its own.
Cashew bark is sold mostly as dried bark chips or a coarse powder. Tinctures and capsules exist but are uncommon.
In West Africa the usual form is a boiled bark water. The same brew was also used as a mouth rinse or a wash for skin.
Never confuse bark products with cashew nut shell liquid. That is a caustic oil that blisters skin. Check the label for the plant part before you buy anything.
Bark products are not tested the way medicines are. No regulator checks their strength or purity.
Cashew trees came from Brazil. Portuguese traders carried them to West Africa in the 1500s. The tree spread fast and became a common village and roadside plant.
Yoruba and other West African healers used bark and leaf brews for loose stools, mouth sores, toothache and high blood sugar. Washes were also used on wounds.
Similar uses were written down in Brazil, India and the Caribbean. The knowledge passed by word of mouth and later into regional plant handbooks.
Stop using it and call emergency services now if your lips, tongue or throat swell, or you struggle to breathe. These are signs of a severe allergic reaction.
Stop and see a doctor the same week if you get a spreading rash or blisters, yellow eyes or skin, dark urine, or black or bloody stools.
See a doctor if you feel shaky, sweaty or confused, which can mean low blood sugar. Also see one if diarrhoea lasts more than two days, or if a toothache or mouth sore is not healing.
In the United States cashew bark may be sold as a dietary supplement, and the FDA does not review it for safety or effect before sale. In the UK and EU it is not an authorised herbal medicine. In much of West Africa it is sold openly in markets as a traditional plant remedy.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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