Educational information, not medical advice — ask your doctor or midwife.
Quina amarga is the wood and bark of Quassia amara, a small tree of tropical Latin America. It is one of the most bitter plants known. People have long taken it as a bitter tonic for poor appetite and an upset stomach.
It is also sold as bitterwood or amargo. Today the wood flavours bitter drinks, and extracts go into some head lice lotions and garden insect sprays.
Human evidence is thin. Long and wide traditional use is not proof that it works, and it is not proof that it is safe. One small trial supports a lice lotion; most other uses rest on tradition, lab tests and animal work.
The bitter taste is the main proposed mechanism. Bitter compounds on the tongue may trigger saliva and stomach juices. In people, this "bitter tonic" effect is still poorly tested.
In lab tests and animal studies, extracts slow some parasites and insects. The bitter compounds appear to act as stomach poisons to lice and larvae. Whether a drink made from the wood does the same inside your gut is not established.
In test tubes, extracts also act against malaria parasites and some bacteria. That is a long way from treating an infection in a person.
In animals, extracts have lowered blood sugar. In male animals, high doses lowered sperm counts and testosterone. Neither finding has been tested properly in people, and the second is a reason for real caution.
Quina amarga is sold in a few simple forms.
- Dried wood chips or shavings, soaked in water to make a bitter drink.
- Powdered wood or bark in capsules.
- Alcohol tinctures and drops, often sold as digestive bitters.
- Bitter aperitifs and tonic drinks, where it is only a flavouring.
- Scalp lotions for head lice, sold mainly in Central America.
- Garden and animal insect sprays, which are never meant to be swallowed.
Strength is not standard across these forms. A home-made soak and a measured tincture are not the same thing.
Many products mix it with other bitters, such as gentian or angostura bark. Read the label for everything in the bottle.
Quassia amara was used across Suriname, Guyana, the Caribbean and Central America. Healers gave the bitter wood for weak appetite, slow digestion and fevers.
The plant carries the name of Graman Quassi, an 18th-century healer in Suriname. He is credited with bringing the remedy to European notice.
The wood entered European pharmacy lists in the 1700s as a bitter tonic. Carved "bitter cups" were sold for home use. Water left standing in the cup turned bitter, and people drank it as a tonic.
It was also given as an enema for threadworms in children, and used as a fly poison. Those are historical practices, recorded here as history, not as advice.
Stop taking it and see a doctor if you get repeated vomiting, bad stomach pain, or burning that does not settle.
Get medical help the same day for any of these:
- Black or tarry stools, or blood in vomit or stools.
- Unusual bruising or bleeding that will not stop.
- Yellow skin or eyes (jaundice), or dark urine.
- Shaking, sweating, or confusion, which can mean low blood sugar.
- A spreading rash, or swelling of the face, lips or throat.
Call emergency services for fever with chills after tropical travel, or for any swelling of the throat or trouble breathing.
In the United States, quassia extract is allowed as a flavouring in alcoholic drinks, and the wood is sold as a dietary supplement. Supplements are not checked for strength or purity before they reach the shelf. In the UK and EU it is permitted as a food flavouring, with limits set on how much quassin a product may contain.
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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