Herbal Monograph
Pau d'Arco
Handroanthus impetiginosus (Mart. ex DC.) Mattos
Bignoniaceae
Amazonian bark renowned for potent antifungal and antimicrobial action, rich in naphthoquinones
Overview
Plant Description
Handroanthus impetiginosus is a medium to large deciduous tree of the family Bignoniaceae, typically growing 8-20 meters tall in cultivation but reaching up to 30 meters in height with trunk diameters of 40-80 cm in its native forest habitat. The trunk is erect with grey-brown, deeply fissured bark; the inner bark (the medicinal part) is fibrous, reddish-brown to tan, and distinctly bitter. The crown is semi-globose to spreading. Leaves are opposite, palmately compound with 5-7 (occasionally 3) leaflets, each elliptical-oblong, 5-12 cm long, with serrate margins and a short-acuminate apex. The tree is deciduous, shedding its foliage before the spectacular flowering period. Flowers are showy, trumpet-shaped (tubular-campanulate), 4-6 cm long, in terminal panicles or corymbs; the corolla ranges from rose-pink to magenta-purple with a yellow throat streaked with darker lines that serve as nectar guides. Flowering occurs en masse from late winter through early spring (July to September in the Southern Hemisphere) when the tree is completely leafless, producing a dramatic visual display that makes the species a popular ornamental. The fruit is a narrow, elongated capsule (siliqua), 15-40 cm long, bearing numerous winged seeds adapted for wind dispersal. The wood is extremely hard, dense (specific gravity 0.9-1.1), and highly durable, making it one of the most valued timber species in the Neotropics. The name 'pau d'arco' translates to 'bow stick' or 'bow wood' in Portuguese, reflecting the indigenous use of this dense wood for crafting bows.
Habitat
Handroanthus impetiginosus occurs in seasonally dry tropical and subtropical forests, semi-deciduous forests, cerrado (tropical savanna) margins, and transitional forests. It thrives in areas with a pronounced dry season of 3-6 months duration. The species prefers well-drained soils and can tolerate a range of substrates from sandy to clay, though it grows most vigorously on deep, fertile alluvial soils. It is found from lowland forests near sea level up to approximately 1200 meters elevation. The tree is a component of both primary and secondary forests and can colonize disturbed areas. It is somewhat drought-tolerant once established and displays moderate frost sensitivity, limiting its cultivation to tropical and warm-temperate zones.
Distribution
The species has a broad Neotropical distribution extending from northern Mexico through Central America and throughout much of South America, south to northern Argentina and Paraguay. It is especially abundant in Brazil (where it is one of the most recognizable native trees), Bolivia, Peru, Colombia, Venezuela, and the Guianas. In Brazil, it occurs across multiple biomes including the Atlantic Forest, Cerrado, Caatinga, and Amazonian transitional forests. The tree has been widely planted as an ornamental and shade tree throughout tropical and subtropical regions worldwide, including southern Florida, Hawaii, the Caribbean, southern Africa, Southeast Asia, and Australia. Wild populations face some pressure from overharvesting of bark for the medicinal trade and from deforestation, though the species is not currently classified as globally threatened (IUCN Least Concern).
Parts Used
Inner bark (entrecasca, liber)
Preferred: Dried shredded inner bark for decoction; powdered inner bark for capsules; hydroalcoholic extract (tincture)
The inner bark of the trunk and major branches is the exclusively used medicinal part in both traditional South American medicine and modern herbal commerce. This thin layer of tissue between the outer bark (rhytidome) and the sapwood contains the highest concentration of bioactive naphthoquinones, particularly lapachol and beta-lapachone. The inner bark is distinguished from the outer bark by its reddish-brown color, fibrous texture, and intensely bitter taste. Ethnobotanical records from the Guarani and Tupi consistently specify the inner bark. Commercial products labeled 'pau d'arco bark' or 'lapacho bark' should ideally contain only inner bark, though adulteration with outer bark and wood is common. The whole outer bark or heartwood contain naphthoquinones at much lower concentrations and are not considered equivalent.
Key Constituents
Naphthoquinones
Naphthoquinones, particularly lapachol and beta-lapachone, are considered the signature bioactive constituents of pau d'arco and are responsible for the herb's most prominent pharmacological activities: antimicrobial (antifungal, antibacterial, antiprotozoal), anti-inflammatory, and antitumor effects. The naphthoquinone content of the inner bark serves as the primary quality marker for commercial products. These compounds are moderately lipophilic and are extracted by both water (decoction, though less efficiently) and alcohol. The intensely bitter taste of authentic pau d'arco bark is largely attributable to its naphthoquinone content. Importantly, the clinical safety profile of whole bark preparations at traditional doses is distinct from that of isolated high-dose lapachol, which caused anticoagulant toxicity in NCI trials. The whole bark contains a complex mixture of naphthoquinones at much lower individual doses than the isolated compound studies.
Benzoic acid derivatives
Benzoic acid derivatives contribute to the overall antimicrobial and antioxidant activity of pau d'arco bark preparations, complementing the more potent naphthoquinone constituents. Their presence supports the traditional topical and internal antimicrobial applications.
Iridoids
Iridoids contribute to the anti-inflammatory and potentially gastroprotective properties of pau d'arco bark preparations. While less pharmacologically prominent than the naphthoquinones, the iridoid content distinguishes pau d'arco chemically from other naphthoquinone-containing plants and may modulate the overall therapeutic effect of whole-bark preparations.
Flavonoids
Flavonoids provide significant antioxidant capacity and anti-inflammatory activity, complementing the naphthoquinone fraction. Quercetin in particular may contribute to the antihistamine and anti-allergic properties attributed to pau d'arco in traditional use. The flavonoid content supports the overall tissue-protective and antioxidant effects of whole-bark preparations.
Steroidal saponins
Steroidal saponins may contribute to the immune-modulating and anti-inflammatory effects of the whole bark. Their surfactant properties could theoretically enhance absorption of co-occurring naphthoquinones in the gastrointestinal tract, though this has not been specifically demonstrated for pau d'arco.
Anthraquinones
Minor constituents that may contribute to the traditional use of pau d'arco bark tea as a mild digestive and detoxifying remedy. Their pharmacological contribution at the concentrations present in bark preparations is likely modest compared to the naphthoquinones.
Herbal Actions
Kills or inhibits the growth of microorganisms
The hallmark pharmacological action of pau d'arco bark. Lapachol and beta-lapachone demonstrate broad-spectrum antimicrobial activity in vitro, encompassing antifungal (Candida albicans, Candida tropicalis, Cryptococcus neoformans, dermatophytes, Aspergillus spp.), antibacterial (Staphylococcus aureus including MRSA, Helicobacter pylori, Streptococcus spp., Clostridium spp., Enterococcus faecalis), antiparasitic (Trypanosoma cruzi, Plasmodium falciparum, Leishmania spp., Schistosoma mansoni), and antiviral (modest activity reported against some enveloped viruses) effects. The antifungal activity is among the most clinically relevant traditional applications: pau d'arco bark tea and topical preparations have been used for centuries against Candida infections (thrush, vaginal candidiasis) and skin mycoses. Castellanos et al. (2009) reviewed the antimicrobial evidence and confirmed significant in vitro activity though noted the gap between laboratory findings and clinical trial data. The antimicrobial mechanism involves disruption of microbial electron transport chains and generation of reactive oxygen species via the quinone redox cycling. Park et al. (2006) demonstrated selective bactericidal activity of inner bark methanol extracts against Helicobacter pylori and Clostridium species.
[1, 2, 7]Reduces inflammation
Pau d'arco bark constituents demonstrate significant anti-inflammatory activity through multiple mechanisms. Beta-lapachone inhibits NF-kB activation, suppressing the production of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) and enzymes (COX-2, iNOS) in activated macrophages and other immune cells. Lapachol inhibits prostaglandin synthesis and 5-lipoxygenase activity. Furanonaphthoquinones isolated from the bark show potent inhibition of TNF-alpha and IL-1beta release in vitro. The iridoid constituents (catalposide) also contribute anti-inflammatory effects via NF-kB suppression. Zhang et al. (2020) comprehensive review confirmed strong anti-inflammatory activity as one of the most well-supported pharmacological properties of T. impetiginosa, with effects demonstrated across multiple in vitro and in vivo models including carrageenan-induced paw edema, LPS-stimulated macrophage models, and collagen-induced arthritis.
[1, 2, 9]Stimulates and enhances immune response
Pau d'arco bark preparations demonstrate immune-enhancing properties, including stimulation of macrophage phagocytic activity, enhancement of natural killer cell function, and modulation of lymphocyte proliferation. Zhang et al. (2020) reviewed the immunopharmacological properties of T. impetiginosa and documented effects on both innate and adaptive immunity. The furanonaphthoquinones and polysaccharide fractions of the bark appear to contribute most significantly to immunostimulant activity. Traditional use as a blood-purifying and constitution-strengthening tonic in South American folk medicine aligns with these immune-supporting properties. The immunostimulant action is classified as secondary rather than primary because the evidence is predominantly in vitro and animal-model based, without robust human clinical trials specifically measuring immune parameters.
[1, 2]Prevents or slows oxidative damage to cells
The flavonoid constituents (particularly quercetin), benzoic acid derivatives, and certain naphthoquinone metabolites contribute antioxidant activity. Bark extracts demonstrate significant free radical scavenging capacity (DPPH, ABTS assays) and inhibition of lipid peroxidation in vitro. The antioxidant activity is classified as secondary because it is not the dominant or most distinctive pharmacological action of pau d'arco -- the naphthoquinones themselves are actually pro-oxidant at higher concentrations (generating ROS via quinone redox cycling), and the anticancer mechanism of beta-lapachone relies on pro-oxidant ROS generation. At typical herbal doses, the net antioxidant capacity of the whole bark extract likely predominates due to the flavonoid and phenolic acid content.
[2, 9]Relieves pain
Analgesic (pain-relieving) activity has been demonstrated in animal models, including writhing test and hot plate assays. The mechanism is likely multifactorial: suppression of inflammatory pain mediators (prostaglandins, bradykinin) via COX and LOX inhibition, and possible central analgesic effects. The clinical trial by Goncalves et al. (2023) in women with primary dysmenorrhea found significant reduction in pain intensity scores with pau d'arco bark capsules (1050 mg/day), supporting the traditional use for pain conditions. Traditional South American use includes application for arthritis, rheumatism, and muscle pain.
[2, 5]Stimulates digestive secretions via bitter taste receptors
The naphthoquinone content, particularly lapachol, imparts a distinctly bitter taste to pau d'arco bark preparations. This bitterness stimulates digestive secretions (saliva, gastric acid, bile) via bitter taste receptor (T2R) activation and the cephalic phase digestive reflex. The bitter quality supports the traditional use of pau d'arco tea as a digestive tonic and appetite stimulant. The intensity of bitterness correlates with naphthoquinone content and serves as a rough quality indicator for bark products -- weakly bitter preparations may be adulterated or derived from inferior plant material.
[1]Tightens and tones tissue, reduces secretions
Mild astringent properties attributed to tannin and flavonoid content. Traditional use includes topical application for wound healing, skin ulcers, and oral thrush, where the astringent action helps to tone and tighten mucous membranes and reduce microbial colonization. The astringent quality supports the cool, dry energetic profile of the herb.
[1, 3]Gradually restores proper body function and increases overall health
Pau d'arco is classified as a blood cleanser (depurativo) in Brazilian and South American folk medicine. The alterative action refers to its traditional reputation for gradually restoring proper function and improving overall health, particularly in conditions of chronic infection, toxic accumulation, or debility. The antimicrobial, anti-inflammatory, and mild laxative properties collectively support this traditional classification. Western herbalists have adopted pau d'arco as an alterative herb for chronic candidiasis, chronic fatigue states, and supportive cancer care.
[1, 3]Therapeutic Indications
Immune System
Candidiasis (oral thrush, vaginal candidiasis, systemic candidal overgrowth)
One of the most prominent traditional and modern applications of pau d'arco. Lapachol and beta-lapachone demonstrate significant antifungal activity against Candida albicans, C. tropicalis, C. parapsilosis, and other Candida species in vitro, with MIC values in the low microgram/mL range. The antifungal mechanism involves disruption of fungal mitochondrial electron transport and generation of intracellular ROS. Multiple in vitro studies confirm the activity, and the traditional use for candidal infections is deeply documented across South American ethnobotanical traditions. Clinical evidence specifically from controlled trials is limited, but the convergence of strong in vitro data, extensive traditional use, and practitioner experience supports this indication.
[1, 2, 3]Recurrent infections and immune support (general)
Traditional use as an immune tonic and blood cleanser (depurativo) for individuals prone to recurrent infections. The immunostimulant properties -- enhanced macrophage phagocytosis, NK cell activity, and lymphocyte proliferation demonstrated in vitro -- provide pharmacological rationale for this traditional use. Pau d'arco is commonly combined with echinacea, astragalus, or medicinal mushrooms in Western herbal immune support formulas.
[1, 2]Parasitic infections (malaria, trypanosomiasis, leishmaniasis)
Lapachol and beta-lapachone demonstrate antiprotozoal activity against Plasmodium falciparum, Trypanosoma cruzi, and Leishmania species in vitro and in some animal models. Traditional Amazonian use includes treatment of malaria and other parasitic diseases. However, in vivo efficacy at achievable oral doses in humans remains undemonstrated in clinical trials. The antiparasitic use should be considered preliminary and supplementary to conventional antiparasitic treatment.
[1, 2]Skin / Integumentary
Fungal skin infections (dermatophytosis, tinea, ringworm)
Topical application of pau d'arco bark decoction or diluted tincture for superficial fungal skin infections is a well-documented traditional use throughout South America. In vitro studies confirm activity against common dermatophytes (Trichophyton spp., Microsporum spp., Epidermophyton spp.). The combination of antifungal naphthoquinones with mild astringent tannins provides a pharmacological basis for topical efficacy.
[1, 2, 3]Wounds, skin ulcers, and boils
Traditional topical application for wound healing, infected ulcers, and boils. The antimicrobial, anti-inflammatory, and mild astringent properties support wound-healing applications. Beta-lapachone has demonstrated wound-healing activity in preclinical models. Guarani and Tupi traditional use includes application of bark preparations to skin lesions and snakebites.
[1, 3]Psoriasis (adjunctive, topical)
Lapachol and beta-lapachone have been described as antipsoriatic agents based on in vitro antiproliferative effects on keratinocytes and anti-inflammatory activity. Some traditional use for psoriatic plaques is documented. Clinical evidence is very limited and insufficient to recommend as primary therapy.
[2]Digestive System
Gastrointestinal infections (bacterial dysentery, gastroenteritis)
Traditional use throughout South America for dysentery, diarrhea of infectious origin, and gastrointestinal infections. Bark tea (decoction) is taken internally. The broad-spectrum antibacterial activity, including against enteric pathogens, provides pharmacological support. Park et al. (2006) demonstrated significant activity of bark extracts against Helicobacter pylori and intestinal Clostridium species.
[1, 3, 7]Helicobacter pylori infection (adjunctive)
Park et al. (2006) demonstrated strong in vitro bactericidal activity of T. impetiginosa inner bark methanol extract against Helicobacter pylori. MIC values were in the range of 50-100 micrograms/mL. No clinical trials have specifically evaluated pau d'arco for H. pylori eradication, but the in vitro data suggest potential as an adjunctive therapy.
[7]Digestive sluggishness and poor appetite
The pronounced bitter taste of pau d'arco bark tea stimulates digestive secretions via the cephalic phase reflex, supporting its traditional use as a digestive tonic and appetite stimulant. This aligns with the broader Western herbal classification of bitter herbs as digestive aids.
[1]Respiratory System
Upper respiratory infections (colds, flu, bronchitis)
Traditional use of pau d'arco bark tea for colds, influenza, cough, and bronchitis is extensively documented across South American ethnobotanical traditions. The antimicrobial, anti-inflammatory, and immunostimulant properties provide pharmacological rationale. No controlled clinical trials have evaluated efficacy for upper respiratory infections specifically.
[1, 3]Musculoskeletal System
Arthritis and rheumatic conditions (adjunctive, anti-inflammatory)
Traditional use for arthritis and rheumatic pain in Brazilian and wider South American folk medicine. The anti-inflammatory mechanisms (NF-kB inhibition, COX-2 and LOX suppression) provide pharmacological rationale. In vivo anti-inflammatory effects have been demonstrated in carrageenan-induced paw edema and other inflammatory models. Clinical trial data specifically for arthritis are lacking.
[2, 3]Reproductive System
Primary dysmenorrhea (menstrual pain)
Goncalves et al. (2023) conducted a single-arm, open-label trial of pau d'arco bark capsules (1050 mg/day for 8 weeks) in 12 women with primary dysmenorrhea. Significant reductions in pain intensity were observed after the first dose (p < 0.01) and continued at 4 and 8 weeks. Pain interference, quality of life, and sexual function improved nonsignificantly. The herb was generally safe with moderate tolerability. This is the first clinical trial specifically investigating pau d'arco for dysmenorrhea. The anti-inflammatory (COX-2 and LOX inhibition) and analgesic properties of naphthoquinones provide mechanistic rationale.
[5]Lymphatic System
Blood purification and detoxification support (depurativo)
Pau d'arco is one of the most widely used 'depurativo' (blood-purifying) herbs in Brazilian and Latin American folk medicine. The concept of blood purification in traditional phytotherapy encompasses elimination of toxins, clearance of chronic low-grade infections, and restoration of healthy tissue function. This traditional indication aligns with the Western herbal concept of an alterative herb. The antimicrobial, anti-inflammatory, mild laxative, and immunostimulant properties collectively support this traditional role.
[1, 3]Energetics
Temperature
cool
Moisture
dry
Taste
Tissue States
hot/excitation, damp/stagnation, damp/relaxation
In Western herbal energetics, pau d'arco is classified as cool and dry, with a predominantly bitter and mildly astringent taste profile. The cooling quality reflects its anti-inflammatory and antimicrobial actions, which counter heat and infection states. The drying quality is expressed through its astringent tone on tissues and its affinity for damp, boggy conditions (candidal overgrowth, chronic mucous discharges, damp skin conditions). The pronounced bitterness stimulates digestive secretions and has a descending, clearing action on the body. Pau d'arco is best suited for conditions characterized by damp heat (infections with inflammation, candidiasis with discharge, infected wounds) and damp stagnation (chronic fungal overgrowth, sluggish metabolism, boggy tissues). It is less appropriate for cold, dry, depleted constitutions unless combined with warming and nourishing herbs. In South American traditional classification, pau d'arco bark is considered a 'depurativo' (blood cleanser) and a 'tonico' (tonic), indicating its role in clearing toxic accumulations and restoring vitality. CAVEAT: Herbal energetics are interpretive frameworks within Western herbalism and traditional Latin American phytotherapy, not standardized across all practitioners.
Traditional Uses
Guarani and Tupi indigenous medicine (Brazil, Paraguay)
- Inner bark decoction (tajy bark tea) taken as a tonic for strength and vigor
- Treatment of fevers, malaria, and infectious diseases
- Topical application for skin infections, boils, wounds, and snakebites
- Internal use for dysentery and gastrointestinal infections
- Treatment of syphilis and other sexually transmitted infections
- General blood-purifying tonic (depurativo) for chronic illness and debility
"The Guarani and Tupi Indians call the tree 'tajy,' meaning 'to have strength and vigor,' reflecting their belief in the tonic and restorative properties of the bark. They used the inner bark decoction for a broad range of conditions including fevers, infectious diseases, dysentery, wounds, and as a general tonic. The dense, resilient wood was used to make bows and other implements, and the tree held cultural significance as a symbol of endurance and vitality."
Brazilian folk medicine (medicina popular brasileira)
- Inner bark decoction for cancer and tumors (one of the most widely cited anticancer folk remedies in Brazil)
- Treatment of Candida infections (oral thrush, vaginal candidiasis)
- Remedy for anemia and blood disorders (depurativo sanguineo)
- Treatment of arthritis, rheumatism, and inflammatory joint conditions
- Remedy for diabetes and metabolic complaints
- Treatment of ulcers (gastric and skin ulcers)
- Internal and topical use for bacterial and fungal skin infections
- Treatment of colds, flu, cough, and respiratory infections
- Remedy for urinary tract infections, prostatitis, and cystitis
- Use for constipation (mild laxative properties at higher doses)
- Adjunctive treatment for sexually transmitted infections (syphilis, gonorrhea)
"Pau d'arco is one of the most widely used medicinal plants in Brazilian popular medicine. The traditional medicine uses of pau d'arco were documented as early as 1873 in Brazilian ethnobotanical records. It is considered a 'planta milagrosa' (miraculous plant) in Brazilian folk tradition, used in decoction form for an extraordinarily wide range of conditions. In the 1960s, reports from Brazil of anticancer effects of pau d'arco tea generated widespread popular and media interest that eventually reached international attention and launched the global herbal trade in this product."
Wider South American traditional medicine (Andean, Amazonian, and folk traditions)
- Treatment of malaria and fevers (widely used across malarial regions of South and Central America)
- Remedy for trypanosomiasis (Chagas disease) in endemic areas
- Topical and internal use for leishmaniasis (skin and visceral forms)
- Treatment of colitis and inflammatory bowel complaints
- Topical wash for eczema, psoriasis, and chronic dermatoses
- Remedy for allergies and chronic inflammatory conditions
"Across South and Central America, the bark of various Tabebuia/Handroanthus species has been used for centuries as a primary remedy for infectious and inflammatory conditions. The use extends beyond Brazilian borders to Bolivia, Peru, Colombia, Paraguay, and Argentina, where the tree is known by various local names including lapacho, taheebo, and ipe-roxo. The breadth of conditions treated reflects both the genuine pharmacological versatility of the bark and the limited access to pharmaceutical medicines in many traditional communities."
[1]
Modern Western herbalism (20th-21st century)
- Primary antifungal herb for chronic and recurrent candidiasis (systemic candida protocols)
- Immune support and antimicrobial herb in formulas for chronic infections
- Alterative (blood cleanser) in protocols for chronic fatigue, fibromyalgia, and immune dysregulation
- Adjunctive supportive herb in integrative cancer care protocols
- Component of antimicrobial and anti-parasitic herbal combinations
- Digestive bitter for sluggish digestion and poor appetite
"Pau d'arco entered Western herbal practice in the 1980s and 1990s following widespread media coverage of its anticancer folk use in Brazil and the pharmacological research on lapachol and beta-lapachone. It is most commonly employed in modern Western herbalism as a primary antifungal herb, particularly in protocols for chronic candidiasis. The American Herbalists Guild and individual practitioners such as David Hoffmann and Stephen Buhner have included pau d'arco in antimicrobial and immune-support protocols. It remains widely available as a bark tea, capsule, and tincture in the herbal supplement market."
Modern Research
Comprehensive review: ethnopharmacology, phytochemistry, and quality control of Red Lapacho
Castellanos et al. (2009) published the definitive ethnopharmacological review of Tabebuia impetiginosa (Red Lapacho/Pau d'Arco) in the Journal of Ethnopharmacology, examining traditional uses, phytochemistry, pharmacological evidence, and quality control issues for this globally traded botanical commodity.
Findings: The review documented extensive traditional use across South American cultures for infectious diseases, inflammation, cancer, and numerous other conditions. Phytochemical analysis confirmed naphthoquinones (lapachol, beta-lapachone), iridoids, flavonoids, and benzoic acids as key constituents. In vitro antimicrobial, anti-inflammatory, and anticancer activities were well supported. However, the authors noted a critical gap between in vitro pharmacological evidence and clinical proof of efficacy: there were no published randomized controlled trials at the time of review. The paper also highlighted significant quality control problems in the commercial market, with variable naphthoquinone content, adulteration, and species substitution being common issues.
Limitations: Narrative review, not a systematic review. Reliance on in vitro and animal data due to absence of clinical trials at time of publication. Quality of some cited ethnobotanical sources is variable.
[1]
Comprehensive review: traditional uses, phytochemistry, and immunopharmacological properties
Zhang et al. (2020) published an updated comprehensive review of T. impetiginosa covering traditional uses, detailed phytochemistry (quinones, flavonoids, naphthoquinones, benzoic acids), and immunopharmacological properties including anti-inflammatory, anti-allergic, anti-autoimmune, and anticancer activities.
Findings: The review identified and catalogued several categories of bioactive compounds, with naphthoquinones as the principal pharmacologically active class. Anti-inflammatory activity was confirmed as one of the strongest and most consistently demonstrated properties across study types. The immunopharmacological activities included: NF-kB pathway inhibition, suppression of COX-2 and iNOS expression, inhibition of MAPK signaling, and modulation of T-cell and macrophage function. The anti-allergic and anti-autoimmune activities were described as emerging areas of research with significant preclinical support.
Limitations: Narrative review. Predominantly in vitro and in vivo (animal) evidence. Clinical trial data remained very limited at time of publication. Species identification issues in the Tabebuia/Handroanthus complex complicate interpretation of some studies.
[2]
Beta-lapachone: natural occurrence, biological activities, toxicity, and synthesis
Hussain et al. (2021) published a comprehensive review of beta-lapachone covering its natural occurrence in Handroanthus/Tabebuia species, physicochemical properties, broad spectrum of biological activities, toxicity profile, and synthetic approaches.
Findings: Beta-lapachone was confirmed as the most pharmacologically potent constituent of pau d'arco bark. Key activities reviewed: (1) Anticancer -- NQO1-dependent mechanism generating futile redox cycling, ROS production, NAD+ depletion, and selective cancer cell death; active against pancreatic, breast, prostate, lung, and colon cancer cell lines in vitro and in xenograft models. (2) Antimicrobial -- antifungal against Candida spp. and antibacterial against MRSA and other resistant organisms. (3) Anti-inflammatory -- NF-kB inhibition, COX-2 suppression. (4) Additional activities: antiobesity, neuroprotective, nephroprotective, wound-healing. Toxicity profile: beta-lapachone showed low toxicity against normal cells (alveolar macrophages, dermal fibroblasts, hepatocytes, kidney cells). Phase I/II clinical trials of ARQ 761 (a clinical formulation of beta-lapachone) for pancreatic cancer were in progress.
Limitations: Review article. The clinical formulation ARQ 761 is a pharmaceutical drug candidate distinct from whole-bark herbal preparations. Results with isolated beta-lapachone at pharmacological doses should not be directly extrapolated to whole-bark tea or supplement use at traditional doses.
[9]
Antibacterial activity against Helicobacter pylori
Park et al. (2006) investigated the antibacterial activity of Tabebuia impetiginosa inner bark methanol extract against Helicobacter pylori and various human intestinal bacteria.
Findings: The inner bark methanol extract demonstrated selective and significant bactericidal activity against H. pylori (a causative agent of peptic ulcers and gastric cancer) with MIC values of 50-100 micrograms/mL. The extract also showed strong activity against Clostridium species (including C. paraputrificum and C. perfringens). Importantly, the extract showed selective inhibition of potentially pathogenic intestinal bacteria while preserving beneficial Bifidobacterium and Lactobacillus species, suggesting a favorable impact on gut microbiome balance. Lapachol and beta-lapachone were identified as the primary active antibacterial compounds.
Limitations: In vitro study only. Antibacterial concentrations achieved in the test tube may not be achievable in vivo through oral dosing of bark preparations. No clinical follow-up study was conducted. Methanol extract preparation differs from traditional decoction.
[7]
Safety and tolerability trial for primary dysmenorrhea
Goncalves et al. (2023) conducted the first clinical trial specifically evaluating pau d'arco (Tabebuia avellanedae) for a clinical indication. This single-arm, open-label trial assessed safety, tolerability, and preliminary efficacy of encapsulated pau d'arco bark (1050 mg/day for 8 weeks) in 12 women aged 18-45 with primary dysmenorrhea.
Findings: The 1050 mg/day dose for 8 weeks was generally safe, with most laboratory markers remaining within normal limits throughout the study. Moderate tolerability was reported, with some mild adverse events. Significant decreases in pain intensity compared to baseline were observed after the first dose (p < 0.01), after 4 weeks (p < 0.01), and after 8 weeks (p < 0.01). Pain interference, quality of life, and sexual function scores improved nonsignificantly. High-sensitivity CRP decreased nonsignificantly, suggesting a trend toward anti-inflammatory effects.
Limitations: Single-arm, open-label design without placebo control. Very small sample size (n=12). No randomization or blinding, limiting causal inference. Short duration (8 weeks, 2 menstrual cycles). Single-center study. Categorized as case-series rather than RCT due to lack of control group.
[5]
Antifungal activity against Candida species
Multiple in vitro studies have evaluated the antifungal activity of lapachol, beta-lapachone, and whole bark extracts against clinically relevant Candida species and dermatophytes.
Findings: Lapachol and beta-lapachone demonstrate significant antifungal activity against Candida albicans, C. tropicalis, C. krusei, and C. parapsilosis with MIC values typically in the 8-64 microgram/mL range. The mechanism involves disruption of mitochondrial electron transport and generation of intracellular reactive oxygen species, leading to fungal cell death. Activity against dermatophytes (Trichophyton spp., Microsporum spp.) has also been confirmed. Beta-lapachone generally shows equal or greater potency compared to lapachol. Whole bark extracts demonstrate activity consistent with their naphthoquinone content, suggesting the parent compounds are the primary antifungal agents.
Limitations: In vitro data. Achievable tissue and serum concentrations after oral dosing of bark preparations are unknown. Comparative efficacy against standard antifungal drugs (fluconazole, nystatin) is generally inferior at equivalent doses. Clinical trials specifically evaluating antifungal efficacy are absent.
Anti-inflammatory mechanisms: NF-kB pathway and cytokine modulation
Multiple studies have investigated the molecular anti-inflammatory mechanisms of T. impetiginosa bark constituents, focusing on NF-kB pathway inhibition and downstream cytokine modulation.
Findings: Beta-lapachone and furanonaphthoquinones from the bark inhibit NF-kB activation in LPS-stimulated macrophages, leading to suppressed transcription of pro-inflammatory genes. Downstream effects include reduced production of TNF-alpha, IL-1beta, IL-6, nitric oxide (via iNOS inhibition), and prostaglandin E2 (via COX-2 suppression). Additionally, MAPK pathway inhibition (ERK, JNK, p38) has been demonstrated. The anti-inflammatory potency of beta-lapachone is comparable to some synthetic anti-inflammatory reference compounds in these assays. The furanonaphthoquinones isolated by Wagner et al. showed particularly potent TNF-alpha and IL-1beta inhibition.
Limitations: In vitro mechanistic studies. Cell culture conditions do not replicate in vivo pharmacokinetics. Concentrations used in vitro may not be achievable through oral dosing. Translation to clinical anti-inflammatory efficacy requires human trials.
NCI clinical investigation of lapachol as anticancer agent (1970s)
The National Cancer Institute (NCI) sponsored Phase I clinical trials of isolated lapachol (NSC-11905) as a potential anticancer agent in the early 1970s, based on promising preclinical antitumor activity in mouse models (Walker 256 carcinosarcoma).
Findings: Lapachol showed significant antitumor activity in several mouse tumor models, leading to clinical investigation. However, Phase I trials revealed that the oral doses required to achieve potentially therapeutic plasma levels (approximately 20-30 mg/kg/day) produced unacceptable side effects, primarily anti-vitamin K anticoagulant activity manifesting as prolonged prothrombin time and bleeding risk (nosebleeds, easy bruising). Nausea and vomiting were also dose-limiting. The NCI concluded in 1974 that the therapeutic window was too narrow for lapachol as an isolated anticancer drug, and clinical development was discontinued. This historical outcome is important context: (1) the anticoagulant toxicity was observed with isolated lapachol at pharmaceutical doses far exceeding those achieved from traditional bark tea consumption, and (2) subsequent research shifted to beta-lapachone and its derivatives (ARQ 761) which have a distinct mechanism and toxicity profile.
Limitations: Historical Phase I trial data from the 1970s. Small patient numbers. Evaluated isolated lapachol, not whole bark. Results do not apply to traditional bark tea doses. The anticancer mechanism of isolated lapachol differs from that of beta-lapachone (the current clinical candidate).
Beta-lapachone (ARQ 761) in oncology clinical trials
Beta-lapachone, reformulated as the clinical candidate ARQ 761 (an intravenous prodrug formulation), has entered Phase I/II oncology clinical trials, primarily targeting pancreatic cancer and other NQO1-overexpressing solid tumors.
Findings: ARQ 761 exploits the overexpression of NAD(P)H:quinone oxidoreductase 1 (NQO1) in many cancer cells. Beta-lapachone is bioactivated by NQO1, creating a futile redox cycle that generates massive levels of reactive oxygen species (ROS), depletes NAD+ and ATP stores, causes extensive DNA damage via PARP1 hyperactivation, and induces a distinctive form of programmed cell death (NQO1-dependent cell death) selectively in NQO1-overexpressing tumor cells. Phase I trials established dose-limiting toxicities (hemolytic anemia in patients with G6PD deficiency) and identified a recommended Phase II dose. Phase II trials for pancreatic cancer in combination with gemcitabine/nab-paclitaxel are ongoing.
Limitations: ARQ 761 is an intravenous pharmaceutical drug candidate, fundamentally distinct from oral herbal preparations of pau d'arco bark. Clinical trial results with ARQ 761 cannot be extrapolated to herbal pau d'arco products. The doses, route of administration, and pharmacokinetics are entirely different. Included here for completeness as the most advanced clinical development of any pau d'arco-derived compound, not as evidence for the herb itself.
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Preparations & Dosage
Decoction
Strength: 15-20 g dried inner bark per 500-750 mL water; approximately 1:30-1:50 herb-to-water ratio
The traditional and preferred preparation method for pau d'arco inner bark. Add 15-20 grams (approximately 1 tablespoon, loosely packed) of dried, shredded inner bark to 500-750 mL (2-3 cups) of cold water. Bring to a boil, then reduce to a low simmer for 15-20 minutes. The prolonged simmering is necessary to extract the naphthoquinones and other water-soluble constituents from the dense, fibrous bark. Strain and drink. The resulting tea will be amber-brown to reddish-brown with a distinctly bitter taste. A second decoction from the same bark material can be prepared by adding fresh water and simmering again for 10-15 minutes. For a stronger preparation, some practitioners recommend simmering for up to 30-40 minutes.
15-20 g dried inner bark per day, decocted in 2-3 cups of water. Drink in 2-3 divided doses throughout the day. Standard therapeutic course: 1-3 cups daily.
2-3 times daily. Decoction may be prepared once daily and divided into portions.
Short-term use for acute infections: 7-14 days. For chronic conditions (candidiasis, immune support): 4-8 weeks, then reassess. Intermittent use with rest periods (e.g., 3 weeks on, 1 week off) is sometimes recommended by practitioners to prevent tolerance and GI irritation.
Not recommended for children under 12 due to lack of pediatric safety data. For adolescents over 12: half the adult dose under practitioner supervision.
Decoction is the traditional South American preparation and the method most consistent with ethnobotanical use. The prolonged simmering extracts naphthoquinones (including lapachol and some beta-lapachone), iridoids, flavonoids, and water-soluble constituents. However, the most lipophilic naphthoquinones are not fully extracted by water alone, which is why some practitioners prefer tincture or dual-extraction preparations. The bitter taste is normal and indicates naphthoquinone content; overly mild-tasting preparations may indicate poor-quality bark. Can be sweetened with honey or blended with complementary herbs (ginger, cinnamon, licorice) to improve palatability. Avoid adding milk or dairy products, as calcium may bind some active compounds.
Tincture
Strength: 1:5, 45-60% ethanol (dried inner bark)
Use dried, finely chopped inner bark. Standard maceration: 1:5 ratio in 45-60% ethanol. The relatively high alcohol content is recommended to efficiently extract lipophilic naphthoquinones (lapachol, beta-lapachone) from the dense bark matrix. Macerate for 4-6 weeks with daily agitation. Press and filter through fine cloth and then filter paper. Store in amber glass bottles away from heat and light.
2-4 mL (40-80 drops) three times daily, diluted in a small amount of water
Three times daily, taken between meals
4-8 weeks for therapeutic courses. Reassess need periodically.
Not recommended for children due to alcohol content and lack of pediatric safety data
Tincture preparation offers superior extraction of the lipophilic naphthoquinones compared to water decoction alone. The higher alcohol concentration (45-60%) is necessary to solubilize lapachol and beta-lapachone from the dense bark material. Tincture is more convenient than decoction for sustained therapeutic use and has a longer shelf life (2-3 years if properly stored). The hydroalcoholic menstruum also extracts flavonoids, iridoids, and water-soluble constituents, providing a broader chemical profile than either water or alcohol alone. Some practitioners use a 1:3 ratio for a more concentrated preparation.
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Capsule / Powder
Strength: Crude powder: 500 mg per capsule. Standardized extract: varies by manufacturer (typically 4:1 to 10:1 concentration ratio)
Dried inner bark, finely powdered (ground to pass through a 40-60 mesh sieve), filled into vegetarian or gelatin capsules. Each capsule typically contains 300-500 mg of powdered bark. Alternatively, concentrated bark extract powder (standardized to naphthoquinone content) may be encapsulated.
Crude powder: 1000-1500 mg (2-3 capsules of 500 mg) two to three times daily. This was the approximate dose range used in the Goncalves et al. (2023) clinical trial (1050 mg/day). Extract capsules: dosage varies by concentration ratio; follow manufacturer specifications or practitioner guidance.
Two to three times daily, taken with meals to reduce potential gastrointestinal irritation
Typical therapeutic course: 4-8 weeks. Reassess need and tolerance periodically.
Not established for children. Not recommended under age 12.
Capsules are the most commercially prevalent form in the Western herbal supplement market. They offer convenience and consistent dosing but have limitations: raw powdered bark may have reduced bioavailability compared to decoction or tincture because the naphthoquinones must be dissolved from the dense bark matrix in the gastrointestinal tract. Extracted (concentrated) bark powders in capsules may offer improved bioavailability. The Goncalves et al. (2023) clinical trial used encapsulated bark and demonstrated both safety and analgesic efficacy at 1050 mg/day. Product quality varies widely; third-party testing for lapachol and beta-lapachone content is recommended. Products should specify that they contain inner bark specifically.
Poultice
Strength: Concentrated decoction: 30-40 g bark per 250 mL water
Prepare a concentrated decoction by simmering 30-40 g dried inner bark in 250 mL water for 20-30 minutes. Strain. Soak clean cotton gauze or cloth in the warm (not hot) decoction. Apply directly to affected skin area. Cover with dry cloth or bandage. Alternatively, mix finely powdered inner bark with enough warm water to form a thick paste. Apply paste directly to skin, cover with gauze.
Apply topically to affected area 2-3 times daily. Leave in contact with skin for 20-30 minutes per application.
2-3 times daily
Until condition resolves, typically 7-14 days for acute infections. Discontinue if irritation develops.
External use may be appropriate for children over 6 under practitioner guidance. Patch test first.
Topical application is a well-documented traditional preparation for fungal skin infections (ringworm, tinea), wounds, boils, and skin ulcers. The direct contact of naphthoquinones with the affected tissue provides locally concentrated antimicrobial and anti-inflammatory effects. Traditional South American practice includes using the decoction as a wash for vaginal candidiasis and as a mouth rinse for oral thrush. The concentrated decoction can also be used as a sitz bath for hemorrhoids or vaginal infections (add 1-2 cups of concentrated decoction to a shallow bath).
Safety & Interactions
Class 2d
Other specific use restrictions apply (AHPA Botanical Safety Handbook)
Contraindications
Although rare, allergic reactions to pau d'arco bark are possible. Individuals with confirmed allergy should not use the product in any form.
Lapachol demonstrates anti-vitamin K (anticoagulant) activity at high doses, as demonstrated in the NCI clinical trials of the 1970s where isolated lapachol at 20-30 mg/kg/day caused prolonged prothrombin time. At standard herbal doses (bark tea or capsules), the lapachol intake is far below these levels and clinically significant anticoagulation is unlikely. However, as a precautionary measure, individuals with active bleeding disorders or on therapeutic anticoagulants should use pau d'arco only under medical supervision. Discontinue at least 2 weeks before elective surgery.
Pau d'arco bark has not been adequately studied for safety during pregnancy. Lapachol has demonstrated embryotoxic and abortifacient effects in animal studies (rats) at high doses. While traditional herbal doses are much lower, the absence of human safety data during pregnancy and the theoretical risk of anticoagulant and uterotonic effects warrants avoidance during pregnancy.
Drug Interactions
| Drug / Class | Severity | Mechanism |
|---|---|---|
| Warfarin, heparin, and other anticoagulants (Anticoagulants) | theoretical | Lapachol has demonstrated anti-vitamin K activity at high doses, potentially increasing anticoagulant effects. At standard herbal doses, lapachol intake is far below the threshold that caused anticoagulation in NCI trials. However, additive effects with pharmacological anticoagulants cannot be excluded. |
| Aspirin, clopidogrel, and other antiplatelet agents (Antiplatelet agents) | theoretical | Potential additive effects on bleeding time due to lapachol's anti-vitamin K activity at high doses. At standard herbal doses, this interaction is theoretical rather than demonstrated. |
| Immunosuppressant medications (cyclosporine, tacrolimus, methotrexate) (Immunosuppressants) | theoretical | Pau d'arco's immunostimulant properties (enhanced macrophage, NK cell, and lymphocyte activity) could theoretically oppose the effects of immunosuppressive drugs. This is a class-wide theoretical concern for immunostimulant herbs. |
Pregnancy & Lactation
Pregnancy
possibly unsafe
Lactation
insufficient data
Pau d'arco should be avoided during pregnancy. Lapachol has demonstrated embryotoxic and teratogenic effects in rats at doses of 100 mg/kg/day, including resorptions and fetal abnormalities. While these doses far exceed standard human herbal intake, the absence of human safety data and the theoretical risks (anti-vitamin K effects potentially affecting fetal coagulation, and possible uterotonic effects) warrant a precautionary avoidance recommendation. Some traditional sources explicitly advise against use during pregnancy. During lactation, there is insufficient data on excretion of naphthoquinones into breast milk or effects on nursing infants. Prudent to avoid therapeutic doses during breastfeeding. Brief, occasional use of dilute bark tea is probably low-risk but not formally evaluated.
Adverse Effects
References
Monograph Sources
- [1] Gomez Castellanos JR, Prieto JM, Heinrich M. Red Lapacho (Tabebuia impetiginosa) -- a global ethnopharmacological commodity?. J Ethnopharmacol (2009) ; 121 : 1-13 . DOI: 10.1016/j.jep.2008.10.004 . PMID: 18992801
- [2] Zhang J, Hunto ST, Yang Y, Lee J, Cho JY. Tabebuia impetiginosa: A Comprehensive Review on Traditional Uses, Phytochemistry, and Immunopharmacological Properties. Molecules (2020) ; 25 : 4294 . DOI: 10.3390/molecules25184294 . PMID: 32962180
- [3] Taylor L. The Healing Power of Rainforest Herbs: A Guide to Understanding and Using Herbal Medicinals. Square One Publishers, Garden City Park, NY (2005) . ISBN: 978-0-7570-0144-6
- [4] Memorial Sloan Kettering Cancer Center. Pau d'Arco: Purported Benefits, Side Effects & More. Memorial Sloan Kettering Cancer Center Integrative Medicine Service (2024)
Clinical Studies
- [5] Goncalves B, Wenner C, Torres S, Olson K, Niihara S, Wilson J, Steel A. Safety and tolerability of Pau d'Arco (Tabebuia avellanedae) for primary dysmenorrhea: A single-arm, open-label trial on adults ages 18-45. Eur J Integr Med (2023) ; 59 : 102231 . DOI: 10.1016/j.eujim.2022.102231 . PMID: 36960315
- [6] Block JB, Serpick AA, Miller W, Wiernik PH. Early clinical studies with lapachol (NSC-11905). Cancer Chemother Rep 2 (1974) ; 4 : 27-28
- [7] Park BS, Kim JR, Lee SE, Kim KS, Takeoka GR, Ahn YJ, Kim JH. Selective growth-inhibiting effects of compounds identified in Tabebuia impetiginosa inner bark on human intestinal bacteria. J Agric Food Chem (2005) ; 53 : 1152-1157 . DOI: 10.1021/jf0486038 . PMID: 15713033
Traditional Texts
- [8] de Melo JG, Santos AG, de Amorim ELC, do Nascimento SC, de Albuquerque UP. Medicinal Plants Used as Antitumor Agents in Brazil: An Ethnobotanical Approach. Evid Based Complement Alternat Med (2011) ; 2011 : 365359 . DOI: 10.1155/2011/365359 . PMID: 21528007
Pharmacopeias & Reviews
- [9] Hussain H, Green IR. Beta-lapachone: Natural occurrence, physicochemical properties, biological activities, toxicity and synthesis. Phytochemistry (2021) ; 187 : 112784 . DOI: 10.1016/j.phytochem.2021.112784 . PMID: 33667813
- [10] Agencia Nacional de Vigilancia Sanitaria (ANVISA). Farmacopeia Brasileira, 6th edition: Monograph on Tabebuia avellanedae (Ipe-roxo). Agencia Nacional de Vigilancia Sanitaria, Brasilia (2019)
Last updated: 2026-03-02 | Status: review
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