pau d'arco

Pau d'Arco (Handroanthus impetiginosus / Tabebuia impetiginosa)

1. Identity

Botanical Classification and Nomenclature

Pau d'arco belongs to the genus Handroanthus, a genus of flowering plants in the family Bignoniaceae, consisting of 30 species of trees known in Latin America by the common names poui, pau d'arco, or ipê. The primary species used medicinally is Tabebuia impetiginosa, also known as Handroanthus impetiginosus (Mart. ex Dc.) Mattos, as accepted on the Plant List. Recognized synonyms include Tabebuia avellanedae, T. ipe, T. nicaraguensis, Handroanthus avellanedae, Tecoma adenophylla, Tecoma avellanedae, and Tecoma impetiginosa, among others.

The genus was initially described under the name Tabebuia by Alphonse Pyramus de Candolle in 1838, marking the formal botanical recognition of these trees within the Bignoniaceae family. In the 20th century the genus underwent significant taxonomic refinement; researchers revealed Tabebuia s.l. to be grossly polyphyletic with multiple independent lineages, and consequently resurrected Handroanthus for a monophyletic clade of 30 species. This revision was published in Systematic Botany (volume 32, issue 3, pages 660–670) and marked a shift toward evidence-based classification in Bignoniaceae. Despite this, the older name Tabebuia impetiginosa remains widely used in the scientific and commercial literature.

Common Names

The species is also known as the pink or purple trumpet tree owing to its flower color. In English it is called Ipe, Taheebo, and purple tabebuia. In French it is known as Poui, while its Spanish names include lapacho negro, lapacho, and quebracho. In German the common names are Lapachobaum, Trompetenbaum, and Feenkraut. In Portuguese the plant is recognized as Pau d'arco (bow tree), Ipe-roxo (red thick bark), and Ipe.

Plant Description and Geographic Distribution

T. impetiginosa is well known due to its conspicuous appearance. This deciduous species can grow to a height of 30 m and sheds its leaves during the dry season. The palmately compound and serrated leaves are green and arranged in opposite or subopposite pairs. It can be found from northern Mexico south to northern Argentina. It is the national tree of Paraguay and is planted in gardens and boulevards as an ornamental tree.

Part Used and Common Preparations

Lapachol and beta-lapachone, isolated from the inner bark of trees used to produce pau d'arco, are thought to be the active constituents responsible for its pharmacological activities. Pau d'arco is sold as tablets, dried bark tea, and tincture (which contains alcohol). Commercial products containing pau d'arco are also available in capsule, extract, and powder forms. Some products are standardized to 3% naphthoquinones, but these indications are not scientifically validated.

The chemicals that give pau d'arco its medicinal effects do not dissolve well in water, so a tea is not the most pharmacologically efficient preparation. Many species of Tabebuia, as well as other completely unrelated tree species exported from South America as "pau d'arco," have few to none of the active constituents of the true medicinal species. Most pau d'arco products are not standardized, so it is hard to determine whether or not they contain a safe amount of these active substances.

2. Traditional and Historical Use

Pre-Columbian and Indigenous Use

Pau d'arco has a long and well-documented history of use by the indigenous peoples of the rainforest, with indications implying that its use may actually predate the Incas. Throughout South America, tribes living thousands of miles apart employed it for the same medicinal purposes for hundreds of years. The name "Pau d'Arco" means "bow stick" in Portuguese, a reference to the traditional use of the tree's wood by indigenous tribes for crafting hunting bows.

The lapacho tree was called "tajy," meaning "the divine tree," and was originally used by indigenous peoples of Paraguay, Brazil, and Bolivia such as the Guarani, Tupinambá, as well as the Incan civilization and their descendants the Kallawaya, a group of traditional healers living in the present-day Bolivian Andes. The Kallawaya were once the naturopathic healers of Incan kings and today are familiar with up to 600 pharmaceutical herbs.

The Guarani and Tupi Indians call the tree tajy, meaning "to have strength and vigor." They used the bark to treat many different conditions and as a tonic for the same strength and vigor it puts into their bows.

Traditional Therapeutic Applications

Pau d'arco is recorded to be used by forest inhabitants throughout the Amazon for malaria, anemia, colitis, respiratory problems, colds, cough, flu, fungal infections, fever, arthritis and rheumatism, snakebite, poor circulation, boils, syphilis, and cancer. Several groups of indigenous peoples in South America also used it for stomach aches, fevers, colds and flu (the leaves), leishmaniasis, dysentery, and diabetes, as well as for "various maladies, especially cancer," as an astringent, and for liver cirrhosis.

The use of pau d'arco as a medicinal herb dates back hundreds of years. Indigenous peoples, particularly in Brazil and Argentina, used the bark to treat a wide range of ailments, from infections and inflammations to gastrointestinal issues and even snake bites. As early as 1873, there are reports of medicinal uses of pau d'arco.

Entry Into Western Medicine

The use of pau d'arco bark was first introduced into Western medicine in the 1960s with early research investigating specific compounds like lapachol, which is known to possess potential antitumor and pain-relieving qualities. In southern areas of Brazil, pau d'arco has been used as a treatment against cancer since the 1960s. Its use was popularized by agronomist and pioneer of Brazilian herbalism, Professor Walter Accorsi, who successfully treated various types of tumours, as well as gastritis and rheumatic pain, with the plant.

In the 1960s, plant extracts of the heartwood and bark demonstrated marked antitumorous effects in animals, which drew the interest of the National Cancer Institute (NCI). Researchers decided that the most potent single chemical for this activity was a naphthoquinone named lapachol, and they concentrated solely on this single chemical in their subsequent cancer research.

3. Key Constituents and Active Compounds

Overview of Phytochemical Classes

Several categories of phytochemicals have been identified in the leaves, bark, and wood of T. impetiginosa. From the bark, 19 glycosides comprising four iridoid glycosides, two lignan glycosides, two isocoumarin glycosides, three phenylethanoid glycosides, and eight phenolic glycosides were methanol-extracted. Major constituents are furanonaphthoquinones, naphthoquinones, anthraquinones, quinones, benzoic acid, flavonoids, cyclopentene dialdehydes, coumarins, iridoids, and phenolic glycosides.

To date, about 292 chemical constituents have been isolated from Tabebuia, among which naphthoquinones are considered the main constituents. Other reported classes of secondary metabolites are tannins, flavonoids, alkaloids, and iridoids.

The plant contains a large number of chemicals known as quinoids, and a smaller quantity of benzenoids and flavonoids. These quinoids — chiefly anthraquinones, furanonaphthoquinones, lapachones, and naphthoquinones — have shown the most documented biological activity and are seen to be the center of the plant's efficacy as an herbal remedy.

Primary Bioactive Compounds: Lapachol and Beta-Lapachone

Lapachol and beta-lapachone (known collectively as naphthaquinones) are two primary active compounds in pau d'arco. Along with lapachol, the extract of the Tabebuia tree contains α-lapachone, β-lapachone, and a newly discovered quinone called xyloidone. Several of the naphthoquinones exhibit strong microbicidal and fungicidal activities. Lapachol has been shown to have both antimicrobial and antiviral activity. Beta-lapachone shows diversified antiparasitic activity as well as antiviral action. Alpha-lapachone is also active against certain parasites, and xyloidone is active against numerous bacteria and fungi.

Pau d'arco bark also contains significant amounts of the antioxidant quercetin. Quercetin, an antioxidant flavonoid, is present in its bark.

Quality and Standardization Concerns

Most of the chemical research on pau d'arco has been done on the wood and not the inner bark. Lapachol isolated from T. avellanedae has exhibited antimicrobial activity, but one research team found that progressive purification reduced the antimicrobial activity of the extract, leading to the conclusion that more than one active substance was present in the original extract. The clinical effects of pau d'arco are difficult to predict because they are influenced by several factors including variation in plant species or plant parts, extraction methods, bioavailability of the active compounds, dosages, and routes of administration.

4. Mechanisms of Action

Anticancer Mechanisms

Beta-lapachone downregulates cyclooxygenase (COX-2) and telomerase activities. It also induces apoptosis in cancer cells via mitochondrial signaling or by activating caspases. The antimetastatic activity of beta-lapachone occurs by inducing Egr-1, known to suppress metastasis, thereby decreasing the invasive ability of cancer cells.

Beta-lapachone is a potent cytotoxic anticancer agent with antitumor activity against a variety of human cancer cells, including drug-resistant cell lines. It is bioactivated by the intracellular enzyme NQO1. NQO1 is differentially overexpressed in several human cancers over normal cells. At optimal concentrations and duration of exposure, beta-lapachone causes DNA damage, inhibits DNA repair, and induces programmed cell death.

A water extract of taheebo showed anti-proliferative effects on hormone-sensitive MCF7 breast cancer cells by modulating gene expression, thereby interfering with cell cycle progression. At high doses, it also has anti-estrogenic effects through the inhibition of estrogen receptor signaling.

Antimicrobial Mechanisms

Lapachol is theorized to block pyrimidine biosynthesis through inhibition of dihydrofolate dehydrogenase. The antitumor activity of lapachol is believed to be due to interaction with nucleic acids. The presumed antifungal activity of lapachol is believed to be due to its interaction with the cellular membrane.

Anti-Inflammatory Mechanisms

Research indicates that pau d'arco chemicals lapachol and β-lapachone help reduce inflammation by inhibiting key inflammatory signaling pathways such as NF-κB and AP-1. These pathways are involved in the production of pro-inflammatory molecules like cytokines and enzymes. By blocking them, pau d'arco extracts can lower the levels of inflammation in the body.

Anticoagulant Mechanism

Lapachol's anticoagulant activity is due to the inhibition of vitamin K epoxide and quinone reductases, an action similar to that of warfarin.

5. Scientific Evidence by Area of Use

5a. Cancer

In studies on beta-lapachone and other quinones in pau d'arco, researchers reported that because of their potent activity against the growth of human keratinocytes, some lapachol-derived compounds appear promising as effective antipsoriatic agents. In a 2002 U.S. patent, beta-lapachone was cited to have significant anticancerous activity against human cancer cell lines including promyelocytic leukemia, prostate, malignant glioma, colon, hepatoma, breast, ovarian, pancreatic, and multiple myeloma cell lines and drug-resistant cell lines.

A 2021 comprehensive review found that beta-lapachone may have potential anticancer, antimicrobial, neuroprotective, and cardiovascular therapeutic properties. Researchers noted that beta-lapachone inhibits tumor growth and suppresses metastasis in cancer cells in in vitro and animal model studies.

A 2023 study on the effects of beta-lapachone on colorectal cancer cells that do not respond to chemotherapy indicated that the compound inhibited the growth of these cells and lowered levels of specific proteins associated with cancer cell multiplication and survival. Researchers could not fully explain the mechanisms of action behind this process. The study was done in vitro, which means the results may not necessarily apply to the human body.

Human/clinical evidence for cancer: Small studies showed that a lapacho-based preparation may help prevent oral mucositis in patients with head and neck cancer undergoing radiotherapy. However, lapachol did not show clinical improvement in patients with chronic myelocytic leukemia. A Phase II study tested Orasol Plus, a lapacho-based nutritional swallowable solution useful to support the defenses of the oropharyngeal mucosa. Between January and June 2014, 40 consecutive adult patients affected by head and neck cancer were enrolled, and Orasol Plus was administered 3 times a day from the first day until the end of radiotherapy. Only 11 (27.5%) of these patients developed oral mucositis Grade 2, and only 4 (10%) developed Grade 3; no patient developed Grade 4. This study was uncontrolled and constitutes preliminary evidence only.

Interest in cancer use was intensified by extensive research in the 1960s that focused on the possible anti-cancer activity of lapachol. However, research studies were stopped because, at the amounts needed to be effective against cancer, pau d'arco might well be poisonous — among other things, it can cause severe internal bleeding. To date, no clinical trial has confirmed the effectiveness of lapacho in treating cancers. Overall, the evidence for pau d'arco as a cancer treatment in humans is negative or insufficient: it is based on in vitro and animal studies, with one failed human trial for leukemia and one small uncontrolled study in a supportive-care context.

5b. Antimicrobial, Antifungal, and Antiviral Activity

Lapachol and beta-lapachone have anti-fungal properties in laboratory tests as potent as ketoconazole, a common antifungal drug. However, amounts of these constituents needed to exert an antifungal effect may be toxic to humans.

An analog of lapachol (furanonaphthoquinone) extracted from tree bark was shown to significantly lower the minimum inhibitory concentration (MIC) against methicillin-resistant Staphylococcus aureus (MRSA) compared to methicillin-sensitive Staphylococcus aureus (MSSA), with the finding statistically significant at p<0.01. Lapachol also showed efficacy against H. pylori, Staphylococcus, Streptococcus, Enterococcus, Bacillus, and Clostridium species with MIC ranging from 1.56 to 25 mcg/ml. In addition, lapachol was reported to have a relevant effect against Candida albicans, Candida tropicalis, and Cryptococcus neoformans, similar in potency to Amphotericin B.

A hydro-alcoholic extract of T. impetiginosa inhibited 36% of Helicobacter pylori growth but had no effect on Campylobacter jejuni.

Human/clinical evidence for antimicrobial use: Laboratory studies showed that pau d'arco has antibacterial and antifungal activities, but it has not been tested in humans for these indications. The antimicrobial evidence base is exclusively in vitro and animal, and no controlled human trials have been conducted.

5c. Anti-Inflammatory and Analgesic Effects

Pau d'arco's long-standing traditional uses for arthritis and other inflammatory conditions have attracted research attention. Bark extracts have demonstrated anti-inflammatory activity and have shown success against a wide range of induced inflammation in mice and rats in laboratory research.

A 2020 research review indicated that beta-lapachone has repeatedly shown anti-inflammatory properties in animal and in vitro studies, which researchers say may hold promise for the management of inflammatory conditions like arthritis, asthma, and inflammatory bowel disease (IBD).

Human/clinical evidence for anti-inflammatory use: In vitro and in vivo studies showed anti-inflammatory properties, but human studies are needed to validate these effects. The anti-inflammatory evidence in humans remains at the level of preliminary suggestion only.

5d. Primary Dysmenorrhea (Menstrual Pain)

A clinical trial registered on ClinicalTrials.gov (NCT04245540) and approved by an Institutional Review Board evaluated Tabebuia avellanedae supplementation of 1,050 mg/day for eight weeks in generally healthy women aged 18–45 with primary dysmenorrhea. A convenience sample of 12 women was recruited. Seventy-five percent of participants (n = 9/12) completed the study. Seventy-five percent reported an adverse event, most characterized as mild, and none were determined to be an FDA serious adverse event. Most laboratory markers stayed within normal limits. There was a statistically significant decrease in pain intensity compared to baseline after the first dose (p<0.01), after 4 weeks of treatment (p<0.01), and after 8 weeks of treatment (p<0.01). Over the 8-week intervention period, pain interference, quality of life, and sexual function scores improved nonsignificantly and hs-CRP decreased nonsignificantly. This was a single-arm, open-label trial without a control group, and the very small sample size (n=12, with only 9 completers) severely limits any conclusions. The study constitutes preliminary safety and feasibility data, not efficacy evidence.

5e. Gastric and Antiulcer Effects

Tabebuia avellanedae is used in traditional medicine for the treatment of peptic ulcers. Researchers carried out studies with the ethanolic extract of bark from Tabebuia avellanedae (at doses ranging from 30–1000 mg/kg) to determine its gastroprotective activity; acute gastric ulceration in rats was produced by oral administration of ethanol and ibuprofen. Administration of the extract significantly inhibited gastric mucosa damage induced by ethanol and ibuprofen. These are animal studies; no controlled human trials on this indication have been published.

5f. Antiparasitic Effects

Although lapachol itself has only weak antiprotozoal properties, a number of synthetic derivatives are more potent. β-Lapachone and allyl-β-lapachone were found to be active against T. cruzi epimastigotes, and the latter was shown to reduce the infectivity of trypomastigotes inoculated into mice. β-Lapachone was not effective in vivo, however, as it reacts with haemoglobin with the formation of methaemoglobin. Evidence for antiparasitic use is restricted to in vitro and animal models.

5g. Neuroprotective and Other Emerging Areas

A 2021 review found that beta-lapachone is effective at fighting bacteria and fungi. It may also protect brain cells, reduce oxidative stress, and lower inflammation, which holds potential for the management of conditions like heart disease, dementia, and Parkinson's disease. One study examined the effect of pau d'arco on health decline measures associated with aging in mice and found that beta-lapachone may aid in preventing age-related decline of muscle and brain functions. All such findings are preclinical.

6. Body Systems and Health Areas

Based on the available traditional use documentation and laboratory research, pau d'arco has been studied or historically used in relation to the following body systems:

• Immune system: Traditionally used as an immune tonic; lapachol and beta-lapachone have shown immunomodulatory properties in laboratory and animal studies.
• Oncology (cancer): Extracts or compounds isolated from T. impetiginosa have been studied for antifungal, anti-psoriatic, antioxidant, anti-inflammatory, and anti-cancer activities in laboratory models.
• Infectious disease (bacterial, fungal, viral, parasitic): In lab tests, the naphthoquinones killed some bacteria, fungi, viruses, and parasites.
• Musculoskeletal and inflammatory: Traditional and laboratory-level evidence for arthritis, rheumatism, and general inflammation.
• Gastrointestinal: Used by several indigenous groups for stomach aches, dysentery, and other gastrointestinal conditions.
• Gynecological: Pau d'arco douching and the use of tampons soaked in an alcoholic extract of lapacho have been shown to be very successful against a wide range of inflammations, such as vaginitis, cervicitis, and cervicovaginitis — though this evidence is limited in human context.
• Nervous system: Preclinical data suggest potential neuroprotective properties of beta-lapachone.
• Dermatology: Some lapachol-derived compounds appear promising as potential antipsoriatic agents.

7. Dosage Forms and Reported Dosages

The appropriate dose of pau d'arco depends on several factors such as the user's age, health, and other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for pau d'arco.

The following dosages have appeared specifically in published studies:

• A single-arm clinical trial administered 1,050 mg/day of encapsulated Tabebuia avellanedae to twelve healthy women aged 18–45 for eight weeks.
• For dysmenorrhea, 1,050 mg of pau d'arco combined with 75 mg of rutin per day for 8 weeks was assessed and was reported to be associated with general safety and moderate tolerability, with no serious adverse effects.
• High doses of lapachol (>1.5 g/day) can cause significant gastrointestinal toxicities and increase the risk of bleeding, particularly in cancer patients.
• In the oral mucositis Phase II study, Orasol Plus (a lapacho-based preparation) was administered 3 times a day from the first day until the end of radiotherapy.

8. Safety Considerations and Drug Interactions

Reported Adverse Effects

A clinical study reported nausea, vomiting, and urine discoloration as adverse effects. Animal models showed that large, chronic dosing of lapachol can cause anemia. Short-term administration of lapachol caused significant reduction in the weight of seminal vesicle in mice. Lapachol also has fetotoxic effects, and oral administration of lapachol caused chromosomal abnormalities in mice.

In the clinical dysmenorrhea trial, seventy-five percent of study participants reported an adverse event, most of which were characterized as mild, and none were determined to be an FDA serious adverse event.

Anticoagulant and Bleeding Risk

Lapachol's anticoagulant activity is due to the inhibition of vitamin K epoxide and quinone reductases, an action similar to that of warfarin. Pau d'arco may increase the risk of bleeding with anticoagulant and antiplatelet drugs, though clinical relevance is not fully established. Taking pau d'arco along with medications that also slow clotting might increase the chances of bruising and bleeding. Such medications include aspirin, clopidogrel (Plavix), diclofenac, ibuprofen, naproxen, dalteparin, enoxaparin, heparin, warfarin, and others.

Reproductive and Developmental Toxicity

Lapachol, one of the active chemicals in pau d'arco, may cause loss of pregnancy. Given the animal evidence of fetotoxicity and chromosomal abnormalities, pau d'arco should not be used during pregnancy. Evidence specifically in breastfeeding humans is absent.

Toxicity at High Doses

The amounts of lapachol and beta-lapachone needed to exert an antifungal effect may be toxic to humans. Although these compounds also have anticancer properties according to test tube studies, the effective amount for this effect may also be toxic. Therefore, pau d'arco cannot currently be recommended as a treatment for cancer.

Standardization and Product Integrity Issues

Many species of Tabebuia, as well as other completely unrelated tree species exported from South America as "pau d'arco," have few to none of the active constituents of the true medicinal species. The inner bark shavings commonly sold in the U.S. are actually by-products of the timber and lumber industries. Most pau d'arco products are not standardized, making it hard to determine whether they contain a safe amount of active substances.

Evidence Gaps

The clinical applications of T. impetiginosa have been poorly researched, and there is a void of information on its mechanisms of action in humans. In vitro and in vivo studies showed a range of biological activities, but human studies are needed to validate these effects. The totality of human clinical evidence for pau d'arco across all indications is sparse and methodologically weak. No large, randomized, placebo-controlled trial has been completed for any indication.

References

• Tabebuia impetiginosa: A Comprehensive Review on Traditional Uses, Phytochemistry, and Immunopharmacological Properties — PMC / Molecules (2020)
• Pau D'arco — Memorial Sloan Kettering Cancer Center Integrative Medicine
• Safety and Tolerability of Pau d'Arco (Tabebuia avellanedae) for Primary Dysmenorrhea: A Single-Arm, Open-Label Trial — ScienceDirect / Advances in Integrative Medicine (2022)
• NCT04245540: Effects of Pau d'Arco in Primary Dysmenorrhea — ClinicalTrials.gov
• Beta Lapachone — ScienceDirect Topics Overview
• Lapachol — ScienceDirect Topics Overview
• Pau d'arco (Tabebuia impetiginosa) — Tropical Plant Database, Rain-Tree
• Pau D'arco: Health Benefits, Side Effects, Uses, Dose & Precautions — RxList
• Pau D'arco Drug Reference — Medscape
• Pau D'arco — PeaceHealth Health Information Library
• Genus Tabebuia: A Comprehensive Review — Arabian Journal of Chemistry
• Pau D'Arco Supplements: What the Research Says — Healthline (2024)
• Handroanthus — Wikipedia
• The Sustainability of Pau d'Arco — Herbal Reality (2026)
• Pau d'Arco Database File (Taylor) — ICA Health
• Pau d'Arco Monograph (Woldu) — ICA Health
• Oral Lapacho-Based Medication: An Easy, Safe, and Feasible Support to Prevent and/or Reduce Oral Mucositis During Radiotherapy for Head and Neck Cancer — Nutrition and Cancer (2015)
• Nature Curing Cancer — Review on Structural Modification Studies with Natural Active Compounds — PMC
• Handroanthus impetiginosus — Plants For A Future (PFAF)
• Handroanthus spp. — CITES CoP19 Proposal Document
• Esteemed by Amazonian Indigenous Communities, Pau D'arco Established Its Uses Throughout Brazil — Pacific Rim College
• Lapacho: Benefits, Dosage, Contraindications — Darwin Nutrition