What is Bitterwood?

Bitterwood is the wood and bark of Picrasma excelsa, a tall tree of Jamaica and nearby islands. It is one of the most bitter plants known. It has been used as a bitter tonic for poor appetite and slow digestion.

You may see it sold as bitter ash, Jamaica quassia or quassia wood. It comes as chips, powder, tincture, and as cups turned from the wood. Tiny amounts are also allowed as a bitter flavour in drinks.

Here is the honest verdict on the evidence. Good human trials of this tree are close to absent. Long traditional use is well recorded, but tradition is not proof that a remedy works, and it is not proof that it is safe.

How does Bitterwood work?

The main idea is that the taste does the work. Bitter taste on the tongue may trigger saliva and stomach juices. This 'bitter reflex' has been studied in people, and results are mixed.

The bitterness comes from compounds called quassinoids. In lab tests, these slow or kill some insects, mites and single-celled parasites. Whether that happens inside the human gut is not established.

Animal work raises a flag rather than a benefit. In rats, quassin lowered testosterone and reduced sperm. That effect has not been measured properly in people, so it cannot be ruled out.

No trial has shown that bitterwood treats any illness in humans.

What forms does Bitterwood come in?

Bitterwood reaches you either as plain wood or as a liquid extract.

- Chips, shavings or raspings for steeping in water.

- Coarse powder.

- Tinctures and bitters made with alcohol.

- 'Bitter cups' turned from the wood, which make any water left in them bitter.

- Scalp rinses and lotions aimed at head lice.

- Garden sprays sold as a plant-based insect treatment.

- A bitter flavour used in small amounts in some drinks.

Strength varies hugely between these forms. A tincture or powder is far stronger than a brief soak of chips.

Labels rarely state how much quassin is present. That makes it hard to know what any one product delivers.

Where it comes from:

Caribbean healers used bitterwood for weak appetite, fever, and gut worms. The wood was cut or shaved, soaked in water, and the bitter liquid was drunk.

Ships carried the wood to Europe from the 1700s. Quassia entered British and American pharmacopoeias as a bitter tonic and a worm remedy. The name honours Graman Quassi, an enslaved healer in Surinam, who made the bark of the related tree Quassia amara famous.

Other past uses had nothing to do with medicine. Brewers used the wood as a cheap stand-in for hops, which some countries then banned. Gardeners soaked the chips to make a fly and aphid spray.

These records show standing in the tradition. They do not show that the remedy helped.

What does Bitterwood help with?

• Poor appetite: This is the classic use, and the evidence is weak. Caribbean and later European practice used a bitter soak before meals to 'wake up' the stomach. Research on bitter taste in general suggests it can raise saliva and gut juices. Results in people are mixed, and effects on how much someone eats are small or absent. No trial has tested Picrasma excelsa for appetite in humans.
• Indigestion and bloating: Tradition treated bitterwood as a digestive tonic for heaviness after food. There are no human trials of this tree for indigestion. Bitters as a class have some supportive study, but the findings are small and inconsistent. Strong doses can do the opposite and irritate the stomach.
• Head lice: This is the use with the most human data, but the data is about a different tree. Small open studies of a Quassia amara tincture, a related South American species, reported good clearance of head lice. Those studies had no control group. Picrasma excelsa has not been tested the same way. Treatments sold in pharmacies for lice have far stronger evidence.
• Intestinal worms (threadworm): Folk practice used bitterwood water against worms, sometimes as an enema. In lab dishes, quassinoids slow some parasites. There is no human trial showing that bitterwood clears worms. Do not use it as an enema. Worms are easily treated with proven medicines from a pharmacy or doctor.
• Fever (traditional use): Caribbean use grouped bitterwood with other bitter 'fever woods'. There is no human evidence that it lowers fever. The quassinoid family is chemically related to compounds studied against malaria, but that is lab work on other plants. A fever that lasts or climbs needs medical care, not a bitter tonic.

What are the side effects of Bitterwood?

• Nausea
• Vomiting, especially with large doses
• Stomach pain or burning
• Cramping and diarrhoea
• Heartburn
• Headache or dizziness
• Skin or scalp irritation from rinses
• Rectal pain and bleeding when used as an enema

Good to know:

Small, food-level amounts are usually tolerated by healthy adults.

The common problems are gut problems, and they rise sharply with dose. Vomiting is the body's normal answer to a large bitter dose.

Serious harm is rare but real. Enema use has caused gut injury, and animal data points to effects on male fertility. Stop at the first sign of pain, bleeding or lasting sickness.

How much Bitterwood should you take?

• Recommended daily: This page describes what labels carry. It is not an amount for you to take. Bitters labels usually list a small amount of the dried wood, often around 0.3 to 0.6 g per dose. Tincture labels often list a few drops to about 1 to 2 ml, before meals. Food flavouring levels are far lower than either. Strong extracts and powders are easy to overdo, and large amounts cause vomiting. Talk to a doctor or pharmacist before using it at all.
• Best time of day: Bitters were traditionally taken shortly before a meal, because the taste is the point. Taken at other times it is unlikely to do much. There is no evidence that any time of day works better.
• With or without food: The traditional pattern was a small bitter dose just before eating. On an empty, sore or acid stomach it can sting. If your stomach is easily upset, this is a reason to skip it rather than to shift the timing.
• Time to effect: If a bitter does anything for appetite, the effect is quick, within minutes of tasting it. There is no reliable timeline, because the effect itself is unproven. For many people it will do nothing at all. A scalp rinse for lice would be judged over days of combing, not hours.
• How long to take it: Traditional use was short, measured in days rather than months. No study has looked at long-term safety in people. The animal findings on testosterone make open-ended use a poor idea. Digestive trouble that lasts more than two weeks needs a doctor, not a longer course.