Lapacho (Pau d'Arco)

Handroanthus impetiginosus (syn. Tabebuia impetiginosa, Tabebuia avellanedae) is a large deciduous tree in the family Bignoniaceae. It can reach 30 metres in height and is recognisable by its striking pink to purple trumpet-shaped flowers, which bloom before the leaves emerge in spring.

The tree is native to a wide range spanning from northern Mexico through Central America and into much of South America, including Brazil, Argentina, Paraguay, and Bolivia. It thrives in tropical and subtropical dry forests and is commonly planted as an ornamental.

The part used medicinally is the inner bark (phloem), which is stripped, dried, and shredded. This material is typically brewed as a decoction — simmered in water — rather than steeped as a simple infusion, because the active compounds are not highly water-soluble.

Key bioactive constituents include the naphthoquinones lapachol and beta-lapachone, along with smaller amounts of other quinones (alpha-lapachone, dehydro-alpha-lapachone), benzoic acid derivatives, flavonoids, and iridoids. The naphthoquinone content varies considerably depending on species, harvest season, and bark preparation method.

Indigenous peoples of South America have used pau d'arco bark for centuries. The Guarani and Tupi peoples of Brazil reportedly used bark decoctions to treat fevers, malaria, fungal infections, skin diseases, and stomach complaints. The common name "lapacho" comes from the Spanish used in Argentina and Paraguay; "pau d'arco" is Portuguese-Brazilian and translates roughly as "bow stick," reflecting the wood's use in making hunting bows.

European colonists and missionaries recorded indigenous uses of the bark as early as the 16th century. By the mid-20th century, lapacho tea had become a popular folk remedy across Brazil, promoted for conditions ranging from candidiasis to cancer.

Interest surged in the 1960s when Brazilian physician Orlando dei Santi reportedly used pau d'arco to treat cancer patients. The U.S. National Cancer Institute subsequently tested lapachol in animal models and early-phase clinical studies. While lapachol showed activity against Walker 256 carcinosarcoma in rats, human trials were abandoned due to unacceptable anticoagulant toxicity at the doses required for antitumour effect.

Since the 1980s lapacho has been marketed globally as a dietary supplement, often with dramatic health claims that far outstrip the available evidence. Regulatory agencies in several countries have issued warnings about unsubstantiated marketing claims for pau d'arco products.

The pharmacological activity of lapacho is attributed primarily to its naphthoquinone content. Lapachol and beta-lapachone are redox-active molecules capable of generating reactive oxygen species (ROS) through futile cycling with cellular reductases. This oxidative stress can damage DNA, disrupt mitochondrial function, and trigger apoptosis in susceptible cells.

Beta-lapachone has received particular attention for its interaction with NQO1 (NAD(P)H:quinone oxidoreductase 1), an enzyme overexpressed in many tumour cell lines. Beta-lapachone is bioactivated by NQO1, generating a burst of ROS that leads to DNA single-strand breaks, hyperactivation of PARP-1, NAD+ and ATP depletion, and ultimately programmed necrosis. This mechanism has been demonstrated in cell culture and animal models but not in human clinical trials.

Antimicrobial effects observed in vitro appear to involve disruption of microbial electron transport chains and inhibition of nucleic acid synthesis. Lapachol and beta-lapachone show activity against Staphylococcus aureus, Candida species, Trypanosoma cruzi, and Plasmodium falciparum in laboratory settings, though effective concentrations are often higher than what oral dosing can achieve in humans.

Anti-inflammatory activity has been linked to inhibition of NF-κB signalling, suppression of COX-2 expression, and modulation of nitric oxide production in macrophages. Again, these findings come from cell and animal studies, and their relevance to humans drinking bark tea or taking capsules is uncertain.

Lapacho is traditionally used as a general tonic and immune-support remedy. In South American folk medicine it is taken for candidiasis and other fungal infections, bacterial infections, parasitic diseases, fever, arthritis, and gastrointestinal complaints.

It is widely marketed as a cancer-fighting herb, based on the cytotoxic properties of lapachol and beta-lapachone observed in laboratory research. There is no clinical evidence that lapacho bark, tea, or supplements are effective cancer treatments in humans. The American Cancer Society and Memorial Sloan Kettering Cancer Center both note the absence of human clinical trial data supporting anticancer claims.

Some practitioners of complementary medicine recommend lapacho for chronic candidiasis, particularly vaginal or oral thrush, citing its in-vitro antifungal activity. While the laboratory data are plausible, no controlled human study has confirmed efficacy for these indications.

Other promoted uses include blood sugar regulation, pain relief, and cardiovascular support. Evidence for all of these applications is limited to preclinical research or anecdotal reports.

The traditional preparation is a bark decoction: roughly 15–20 grams of dried inner bark simmered in one litre of water for 15–20 minutes, then strained. This tea is typically consumed in small cups throughout the day. Because the key naphthoquinones are poorly water-soluble, traditional decoctions likely deliver only a fraction of the bark's bioactive compounds.

Commercial preparations include dried bark for tea, powdered bark capsules (typically 500–1500 mg per capsule), liquid tinctures and extracts, and standardised tablets. Standardisation, when present, is usually based on total naphthoquinone content, but there is no consensus on appropriate dose or standardisation target.

Suggested supplement doses in the marketplace typically range from 1,000 to 3,000 mg of dried bark per day, divided into two or three doses. These recommendations are based on traditional practice, not clinical trial evidence. There is no established safe and effective dose for any medical condition.

Topical preparations — poultices, washes, and creams containing pau d'arco extract — are used in folk medicine for skin infections, wounds, and inflammatory skin conditions. Clinical data on topical use are essentially nonexistent.

At doses commonly used in teas and low-dose supplements, lapacho is generally considered well tolerated. However, systematic safety data from human studies are lacking, so the true side-effect profile is poorly characterised.

The most commonly reported adverse effects are gastrointestinal: nausea, vomiting, and diarrhoea, particularly at higher doses. These effects were prominent in the early NCI clinical studies of purified lapachol, where nausea was dose-limiting.

Lapachol has demonstrated vitamin K antagonist activity in animal studies, leading to prolonged prothrombin time and increased bleeding risk. This anticoagulant effect was a major reason the NCI discontinued clinical trials. People with bleeding disorders or those taking anticoagulant or antiplatelet medications should avoid lapacho.

Other reported effects include dizziness, skin rash, and anaemia with prolonged high-dose use. Because naphthoquinones are redox-active and can generate free radicals, there is theoretical concern about hepatotoxicity and nephrotoxicity with chronic use, though documented cases are rare.

Lapacho should not be used during pregnancy. Lapachol has shown embryotoxic and teratogenic effects in animal studies, and the bark's safety during human pregnancy has not been established. Breastfeeding mothers should also avoid it due to the absence of safety data.

People with bleeding disorders, thrombocytopenia, or any condition requiring anticoagulant therapy should avoid lapacho because of the demonstrated vitamin K antagonist effects of lapachol.

Individuals scheduled for surgery should discontinue lapacho at least two weeks before the procedure to reduce the risk of excessive bleeding.

People with liver or kidney disease should use extreme caution, as the naphthoquinones in lapacho are metabolised hepatically and the safety profile in organ impairment is unknown.

Lapacho may potentiate the effects of anticoagulant drugs (warfarin, heparin, direct oral anticoagulants) and antiplatelet agents (aspirin, clopidogrel) due to the vitamin K antagonist activity of lapachol. Combined use increases the risk of bleeding.

Concurrent use with non-steroidal anti-inflammatory drugs (NSAIDs) may further elevate bleeding risk through additive inhibition of platelet function.

Theoretically, lapacho could interact with drugs metabolised by cytochrome P450 enzymes. In-vitro studies suggest lapachol and beta-lapachone can inhibit certain CYP isoforms, but the clinical significance of this interaction is unknown at typical supplement doses.

Patients undergoing chemotherapy or radiation therapy should consult their oncologist before using lapacho. The antioxidant and redox-cycling properties of naphthoquinones could theoretically interfere with treatments that rely on oxidative damage to kill cancer cells.