Pau d'arco is the name of a tea derived from the bark of several Tabebuia species. There are over 100 species of evergreen trees and shrubs in the Tabebuia genus, all of them native to tropical regions of Central and South America. Pau d'arco often comes from Tabebuia avellanedae, a tree found in the Amazonian rain forest. However, according to some, the correct scientific name for pau d'arco is Tabebuia impetiginosa. Other sources claim that Tabebuia chrysata is also marketed in the United States as pau d'arco.

Traditional herbalists in the Brazilian Amazonian rain forest make an infusion from either Tabebuia avellanedae or Tabebuia altissima to treat ulcers, diabetes, rheumatism, cancer, and ringworm. The popularity of this tree for treating cancer, malignant tumors, and Candida fungal infections has soared over the past decade. Increasing demand for pau d'arco has only intensified stripping the bark from the trees, making Tabebuia one of the most exploited plant groups in the Amazon. Tabebuia species are now seriously threatened by extinction.

Extracts of Tabebuia avellanedae have anti-inflammatory, antimicrobial, and anticancer effects. The inner part of the bark supposedly contains lapachol, an active principle that has been shown to be an effective anticancer agent. However, the scientific evidence for the anticancer effects of pau d'arco is weak. While the bark of Tabebuia species does contain lapachol derivatives, only trace amounts of the anticancer compound, lapachol, are actually present. To further complicate matters, most of the research on the chemistry of Tabebuia has been done on the heartwood rather than the bark. But it is the bark that is medicinally important. Critics point out that the relatively high cost and lack of evidence to support therapeutic claims, combined with the fact that pau d'arco is potentially an endangered species, make it a less-than-desirable herbal supplement.

Most species in the Tabebuia genus are broad-leaf evergreen trees. Tabebuia avellanedae grows to a height of 125 feet and is distinguished by rose-to-violet colored flowers. It has exceptionally hard wood that is disease-resistant and does not easily decay.

• Inner bark

Tabebuia avellanedae heartwood: naphthoquinones (lapachol, 2 to 7%; menaquinone-1, deoxylapachol, beta-lapachone, alpha-lapachone, dehydro-alpha-lapachone); anthraquinones (2-methylanthraquinone, 2-hydroxymethylanthraquinone, 2-acetoxymethylanthraquinone, anthraquinone-2-aldehyde, 1-hydroxyanthraquinone, 1-methoxyanthraquinone, 2-hydroxy-3-methylquinone, tabebuin).

Pau d'arco products are not usually standardized for lapachol or naphthoquinone content. Some pau d'arco herbal teas are not authentic, but are derived from the bark of Tecoma curialis. Since Tabebuia and Tecoma species are in the same botanical family (Bignoniaceae), they often contain some of the same active principles. Consequently, remedies made from Tecoma and Tabebuia tree bark sometimes have similar therapeutic activities.

Traditional: tonic, blood builder, rheumatism, cystitis, prostatitis, bronchitis, gastritis, ulcers, liver disorders, asthma, gonorrhea, ringworm, hernias; breast, liver, and prostate cancers

Traditional herbal actions: immune tonic, antimicrobial, antifungal, antineoplastic, antiviral

Clinical applications: cancer, Candida albicans infections (used internally and topically for internal and topical vaginal candidiasis), oral thrush candidiasis, infections of the genitourinary tract (cystitis, prostatitis), herpes, stomatitis, lupus, Hodgkin's disease

In the mid 1950s, Brazilian researchers reported that lapachol isolated from Tabebuia avellanedae had antimicrobial effects against gram-positive and acid-fast bacteria. Lapachol also showed strong antimicrobial effects against Brucella, and it had fungistatic (fungus-inhibiting) properties. However, these effects decreased as the extract was progressively purified to yield a higher content of lapachol but lower quantity of other constituents. Ongoing studies have since confirmed that Tabebuia avellanedae extracts contain not only lapachol, but other active constituents as well. These additional compounds include active quinones such as alpha-lapachone, beta-lapachone, and xyloidone.

Lapachol and other quinones in Tabebuia avellanedae showed antiviral activity against herpes simplex types I and II, influenza virus, poliovirus, and vesicular stomatitis virus. Beta-lapachone produced an antiviral effect by blocking crucial viral enzymes, including DNA and RNA polymerases, as well as retrovirus reverse transcriptase.

Lapachol also had antiparasitic activity against the larvae that cause schistosomiasis, a water-borne disease. When taken orally, lapachol is secreted into the skin where it provides a barrier to the larvae of schistosomes. Beta-lapachone destroys the parasite responsible for trypanosomiasis (Chagas' disease).

In other studies, pau d'arco extracts were effective in reducing inflammation associated with cervicitis and cervicovaginitis. Although extracts reportedly had low toxicity in several investigations, lapachol is known to be toxic when administered as an isolated active principle. Lapachol destroys vitamin K activity. Interestingly, pau d'arco contains a vitamin K–like compound that probably compensates for the anti–vitamin K action of lapachol. This may explain why remedies made from the whole plant do not interfere with vitamin K activity.

In in vivo studies, lapachol exhibited anticancer effects against Walker 256 carcinosarcoma, Yoshida sarcoma, and Murphy-Sturm lymphosarcoma. Despite these promising results, lapachol is not a practical cancer therapy. When given at therapeutically effective doses, lapachol produces the adverse side effects of nausea, vomiting, anemia, and a tendency to bleed. Monkeys given daily doses of 0.0625 to 0.25 g/kg of lapachol developed severe anemia, especially during the initial two weeks of treatment.

Lapachol seemed to be a promising new drug when phase I clinical trials on its safety were first launched at the National Cancer Institue (NCI) in 1968, but researchers soon discovered that therapeutic doses produced mildly toxic side effects. There have been no clinical investigations on the efficacy of lapachol for treating cancer and other diseases because this compound is too toxic for human consumption. However, the anthraquinones in pau d'arco exhibited vitamin K–like activity. It is possible that anti–vitamin K adverse side effects may not have occurred in the NCI study had the whole plant been used instead of lapachol, the isolated compound.

• One cup decocted bark 2 to 8 times/day (1 tsp. pau d'arco boiled in 1 cup water for 5 to 15 min)
• Tincture (1:5): 1 ml tid or qid
• Capsules: 1,000 mg tid

• Large doses can cause nausea.
• Whole bark decoctions do not appear to be toxic for human consumption even though lapachol, one of the active constituents, causes adverse side effects.

Individuals prone to blood-clotting conditions should consult with their health care practitioner before using pau d'arco.

No clinically significant interactions between pau d'arco and conventional medications are known to have been reported in the literature to date.

The U.S. FDA classifies pau d'arco as a dietary supplement.

Anesini C, et al. Screening of plants used in Argentine folk medicine for antimicrobial activity. J Ethnopharmacol. 1993;39:119-128.

Block J, Sterpick A, Miller W, Wiernik P. Early clinical studies with lapachol (NSC-11905). Cancer Chemother Rep. 1974;4(part 2):27-28.

Gershon H, Shanks L. Fungitoxicity of 1,4-naphthoquinones to Candida albicans and Trichophyton mentagrophytes. Can J Microbiol. 1975;21:1317-1321.

Duke J, Vasquez R. Amazonian Ethnobotanical Dictionary. Boca Raton, Fla: CRC Press; 1994:164.

Kinghorn AD, Balandrin MA, eds. Human Medicinal Agents from Plants. Washington, DC: American Chemical Society; 1993:16-17.

Murray MT. The Healing Power of Herbs: The Enlightened Person's Guide to the Wonders of Medicinal Plants. 2nd ed. Rocklin, Calif: Prima Publishing; 1998:220-227.

Nakona K, et al. Iridoids from Tabebuia Avellanedae. Phytochemisty. 1993;32:371-373.

Perez H, et al. Chemical investigations and in vitro antimalarial activity of Tabebuia ochracea ssp. neochrysanta. Intl J Pharmacognosy. 1997;35:227-231.

Schultes RE, Raffauf RF. The Healing Forest: Medicinal and Toxic Plants of the Northwest Amazonia. Portland, Ore: Dioscorides Press; 1990:107-109.

Shealy CN. The Illustrated Encyclopedia of Healing Remedies. Dorset, England: Element Books; 1998:132.

Tyler VE. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Binghamton, NY: Pharmaceutical Products Press; 1994:180.

Tyler VE. The Honest Herbal: A Sensible Guide to the Use of Herbs and Related Remedies. 3rd ed. Binghamton, NY: Pharmaceutical Products Press; 1993:239-240.

Ueda S, et al. Production of anti-tumour-promoting furanonaphthoquinones in Tabebuia avellanedae cell cultures. Phytochemistry. 1994;36:323-325.