YahGarden

Herb library · Herb · Quassia amara

Quassia

An intensely bitter wood from a small tropical American tree, used as a bitter tonic and, in Europe, as a head-lice rinse. Small trials of quassia gels on the skin and of quassia tincture for head lice reported good results, but none was placebo-controlled.

Traditional use

Native to Central America and northern South America and recorded in use across the Guiana shield since at least the 18th century. In a 2021 survey of 1,566 people in eastern French Guiana, it was by far the most cited plant taken for malaria, by every cultural group. It spread through colonial trade as a bitter tonic for poor appetite and digestion, and in Europe a quassia tincture or vinegar was used against head lice.

What studies show

  • Limited

    Head lice: in a Danish series of 454 people, two applications of quassia tincture a week apart left live lice in only three, who appeared to have been reinfested. There was no comparison group.

  • Limited

    Skin (rosacea, seborrheic dermatitis): an open-label study of 30 people with rosacea and a randomized double-blind trial of 60 people with facial seborrheic dermatitis, both from one research group in Argentina, reported that a 4% quassia gel worked as well as or better than standard creams. Neither had a placebo arm.

  • Insufficient

    Digestion and malaria: no trial of quassia taken by mouth in people was found.

Be careful of

Cautions

  • NoteNo modern safety data for quassia taken by mouth were found. Keep the skin and lice preparations out of the eyes.
  • InteractionQuassia appears in reviews of herbs with possible interactions with warfarin. If you take a blood thinner, ask before using it by mouth.
  • PregnancyNo safety information for pregnancy or breastfeeding was found; avoid taking it by mouth then.
  • Ask a clinicianTalk with a clinician or pharmacist before using this if you take prescription medicines, are pregnant or breastfeeding, or are giving it to a child.

Sources

  1. Pediculosis capitis treated with quassia tincture (Acta Derm Venereol, 1978) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  2. Evaluation of the efficacy and tolerance of a topical gel with 4% quassia extract in the treatment of rosacea (J Clin Pharmacol, 2012) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  3. Efficacy of topical 4% Quassia amara gel in facial seborrheic dermatitis: a randomized, double-blind, comparative study (J Drugs Dermatol, 2013) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  4. Potential interactions between alternative therapies and warfarin (Am J Health Syst Pharm, 2000) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  5. Geopolitics of bitterness: Deciphering the history and cultural biogeography of Quassia amara L. (J Ethnopharmacol, 2021) — PubMed record (opens in a new tab) · NIH · read September 25, 2026
  6. When local phytotherapies meet biomedicine: knowledge and intercultural practices against malaria in Eastern French Guiana (J Ethnopharmacol, 2021) — PubMed record (opens in a new tab) · NIH · read September 25, 2026

Reviewed September 25, 2026.