What is Quassia?

Quassia refers primarily to Quassia amara and Picrasma excelsa, two closely related tropical trees native to Central and South America and the Caribbean. The bark and heartwood are among the most intensely bitter substances known in nature, which is precisely what gives the plant its medicinal character. It has been used for hundreds of years by indigenous peoples and traditional healers across Brazil, Suriname, Jamaica, and Guyana as a traditional remedy for digestive complaints, fevers, and intestinal worms.

How does Quassia work?

The bitter compounds in Quassia — especially quassin and neoquassin — are thought to stimulate the production of digestive juices including stomach acid, bile, and digestive enzymes by activating bitter taste receptors in the gut. These same compounds may interfere with the energy production of parasites and malaria-causing organisms, and are traditionally thought to exert a degree of selective toxicity toward these organisms. Quassin is also thought to have a mild effect on the liver, potentially encouraging bile flow and supporting fat digestion, though clinical confirmation in humans remains limited.

What forms does Quassia come in?

Traditional preparations use the wood chips or bark simmered into a tea or decoction. Modern supplement forms include standardized liquid extracts, tinctures, and encapsulated powders. Some traditional preparations are made in wooden cups carved from quassia wood — water left in these cups overnight takes on a bitter, medicinally active brew. Tinctures are the most commonly available commercial form in the West.

Where it comes from:

Quassia amara is named after Graman Quassi, an enslaved man from Suriname who used the plant to treat fevers in the 1730s and shared his knowledge with European botanists. It was formally introduced to European medicine in the 18th century and was listed in several national pharmacopoeias as a digestive bitter and tonic. Before synthetic insecticides, quassia extracts were widely used in agriculture as a natural insecticide — a use that continues today in organic farming.

What does Quassia help with?

• Poor digestion and low stomach acid: Quassia's extreme bitterness is thought to trigger bitter taste receptors throughout the digestive tract, which may signal the body to increase production of stomach acid, bile, and digestive enzymes. Practitioners have traditionally used it as an herbal bitter for people who feel heavy after meals, burp frequently, or struggle to break down rich foods, though these effects have not been confirmed in rigorous clinical trials.
• Loss of appetite: Quassia has a long traditional history as an appetite tonic, and the bitter stimulation it provides is thought to prime the digestive system and signal readiness for food. Traditional practitioners have used it for people recovering from illness, older adults with reduced hunger, or those whose appetite has been blunted by stress or medication, though clinical evidence supporting this use remains observational at best.
• Intestinal parasites and worms: Quassin and related compounds are thought to disrupt the energy metabolism of parasitic organisms, potentially making the gut a less hospitable environment for pinworms, roundworms, and giardia-like organisms. Quassia has been traditionally used as an antiparasitic remedy for centuries across South America and the Caribbean, and preliminary laboratory research has begun exploring the mechanisms behind this traditional application, though well-controlled human trials are lacking.
• Malaria support: Simalikalactone D, a compound isolated from Quassia amara leaves, is thought to have anti-malarial activity, particularly against chloroquine-resistant strains of Plasmodium falciparum. Some preliminary research has explored this further, but evidence remains at an early stage and Quassia should not be considered a replacement for conventional malaria treatment. This is among the more scientifically explored traditional uses of the plant, though findings are not yet clinically validated.
• Liver and gallbladder sluggishness: Quassia is thought to have a mild cholagogue effect, meaning it may encourage the liver to produce more bile and support its release into digestion. Traditional practitioners have used it for feelings of heaviness after fatty meals and to support overall digestive function, though human clinical evidence for direct liver or gallbladder benefit is currently observational only.
• Bloating and indigestion: By potentially improving the flow of digestive secretions, Quassia has traditionally been used to help reduce gas and bloating associated with sluggish digestion. Practitioners have long observed it working best when bloating appears linked to under-digestion rather than food sensitivity, though this distinction and the remedy's effectiveness have not been confirmed in controlled clinical studies.
• Head lice (topical): Topical quassia preparations — typically a strong infusion applied to the scalp — have been used traditionally as a natural treatment for head lice, and some small preliminary studies have explored this application. The plant is thought to act as a natural insecticide and is generally considered well tolerated on skin and scalp, though the evidence base remains limited and larger, well-designed trials are needed before efficacy can be firmly established.
• Fever: Quassia has been traditionally used as a fever remedy in Caribbean and South American herbal practice for centuries, a use plausibly connected to its antimicrobial and anti-malarial properties. This application is well-established in traditional and observational records, though Quassia is not used as a primary fever treatment in modern clinical settings and its effectiveness for this purpose has not been validated in controlled human studies.

What can Quassia help prevent?

• Recurrence of intestinal parasite infection (when used as a periodic cleanse in endemic areas)

Which foods are rich in Quassia?

Quassia is an isolated tree bark and wood extract — it is not found in common foods. However, supporting your digestive system through similar bitter-stimulating foods can complement Quassia's effects. Eating bitter greens like arugula, radicchio, dandelion greens, and endive activates the same bitter taste receptors in the gut, stimulating bile and digestive enzyme production. Including fermented foods like sauerkraut, kimchi, and apple cider vinegar also supports stomach acid levels and digestive motility. Avoiding heavily processed, high-sugar diets is especially important alongside anti-parasitic treatments, as sugar can feed parasitic organisms and undermine the treatment. Garlic and papaya seeds have traditional reputations as anti-parasitic foods that may complement Quassia's effects.

What are the side effects of Quassia?

• Nausea or vomiting at high doses
• Stomach irritation or cramping
• Low blood sugar (hypoglycemia) with excessive use
• Potential reduction in sperm quality or testosterone with long-term high-dose use
• Uterine stimulation: avoid during pregnancy
• Scalp irritation with topical use (uncommon)

Good to know:

Quassia is generally safe when used at recommended doses for short periods. Problems tend to arise with high doses or very prolonged use. It is not recommended during pregnancy due to reported concern over its uterine-stimulating properties.

How much Quassia should you take?

• Recommended daily: Tincture (1:5): 1–2 mL up to three times daily. Dried bark decoction: 1–2 g of wood chips simmered in water, taken 2–3 times daily. Standardized capsules: typically 300–500 mg per dose, follow product label. Topical (head lice): strong decoction applied to scalp and left for 10–15 minutes.
• Best time of day: Take digestive doses 15–30 minutes before meals to maximize bitter-receptor stimulation and digestive enzyme priming.
• With or without food: Take before meals for digestive and appetite benefits. Anti-parasitic protocols are often taken on an empty stomach for maximum gut exposure.
• Time to effect: Digestive effects: 1–2 weeks. Anti-parasitic effects: assess after 2–4 weeks. Head lice: typically 1–2 applications over one week.
• How long to take it: Limit continuous internal use to 4–8 weeks. Cycle off for at least 4 weeks before repeating. Not recommended for continuous long-term use due to potential effects on reproductive hormones and gastrointestinal lining. Topical use does not carry the same restriction.