Pau d’Arco (Lapacho)

What Pau d’Arco is

Pau d’Arco, also called lapacho or taheebo, is the inner bark of Tabebuia impetiginosa, now botanically Handroanthus impetiginosus. The tree grows in the Amazon region and other parts of South America. There the bark is traditionally drunk as a decoction against bacterial and fungal infections, fever, malaria and stomach and bladder complaints (Gómez Castellanos 2009).

In the 1960s, the Brazilian press reported alleged cures of cancer patients; at around the same time, the US National Cancer Institute included the plant in its screening program for anticancer agents. In Germany, lapacho is known mainly as a tea. In the BK-Score, human evidence stands at 2 out of 10 points. This axis rates the state of knowledge, not the plant: drunk for a long time does not mean studied.

How it is supposed to work

The most important constituents are naphthoquinones, above all lapachol and beta-lapachone. In cell and animal experiments, extracts have anti-inflammatory, antibacterial and antifungal effects, and beta-lapachone is additionally strongly cytotoxic to tumor cells (Zhang 2020; Gómez Castellanos 2009). As an isolated compound, beta-lapachone made it as far as phase 2 clinical trials (Zhang 2020).

Between the lab finding and the teacup, the link is missing: how much lapachol or beta-lapachone from tea or capsules actually reaches the body has not been described for the bark in humans. In addition, according to one review, the commercial product varies greatly in quality and composition (Gómez Castellanos 2009).

What the studies show

Menstrual pain: twelve women, no control group

McClure 2022 gave twelve healthy women aged 18 to 45 with primary menstrual pain 1,050 mg of Pau d’Arco daily in capsules for eight weeks. The study was open-label and had no comparison group; the focus was on safety and tolerability. Nine of twelve completed the study, nine reported adverse events, mostly mild and none serious. Among other things, clotting time and blood count were measured; laboratory values remained mostly within the normal range, with isolated slight deviations. Pain intensity decreased compared with baseline. Without a placebo group, this cannot be separated from a placebo effect, and the authors themselves speak of moderate tolerability.

Lapachol in cancer research in the 1970s

The National Cancer Institute tested the single compound lapachol in early clinical trials (Block 1974). These trials concerned an isolated compound, not the bark or the tea, and they did not lead to an approved cancer drug.

Lapachol in animal experiments: severely harmful to the fetus

Guerra 2001 gave pregnant rats lapachol by gavage from day 8 to day 12 of gestation. The mothers remained unremarkable, but 99.2 percent of the fetuses died. Felício 2002 found no harm to the mothers when the substance was given shortly before birth, but delayed growth of the fetuses.

Where the data stop

• Cancer. A controlled study with lapacho tea or capsules in cancer patients could not be found. Lab findings on beta-lapachone and early trials with pure lapachol say nothing about the bark.
• Candida and other fungal infections. Antifungal effects exist only in the lab; clinical studies with oral intake could not be found.
• Menstrual pain. The only human study had twelve participants and no placebo group.
• Product quality. Because composition and active compound content vary, it is impossible to say what a given product contains.

Status, approval and legal

In Germany, lapacho is not a medicinal product. The substance list of the German federal government and the federal states (as of 2014) lists the bark of Tabebuia impetiginosa with known use as a tea and does not assign it to any of the lists on which use in food is discouraged or a restriction is recommended. It names the naphthoquinones, such as lapachol, as critical constituents and points out in general that extracts can differ from the plant itself. The plant has no entry in the EU Commission’s Novel Food Catalogue; whether bark powder or extract in capsules is to be assessed in the same way as tea has not been explicitly clarified by the authorities. There is no authorized health claim. Advertising against cancer, fungi or infections is therefore not permitted.

Safety

Safety has barely been studied systematically. The clearest signals come from animal experiments: lapachol killed almost all fetuses in pregnant rats. A disruption of the vitamin K cycle, which the body needs for blood clotting, has also been described for the bark (more on vitamin K on the page about vitamin K2); this particularly affects people who take anticoagulants. The BVL substance list mentions irritation of the skin and mucous membranes and, in large amounts, cytotoxic effects and disorders of the digestive tract. In the only human study, nine of twelve women reported mostly mild adverse events.

Pregnancy, breastfeeding and the use of anticoagulants are therefore a case for consulting a physician. In the BK-Score, safety data stand at 3 out of 10 points; this axis measures how well safety has been studied, not how safe the plant is. This text is information and does not replace medical advice.

Sources

• Gómez Castellanos JR et al., J Ethnopharmacol 2009 – review of red lapacho (Tabebuia impetiginosa)
• Zhang J et al., Molecules 2020 – review of Tabebuia impetiginosa: tradition, constituents, immunopharmacology
• McClure C et al., Adv Integr Med 2022 – Pau d’Arco for menstrual pain, open-label study with 12 women
• Block JB et al., Cancer Chemother Rep 2 1974 – early clinical trials with lapachol (NSC-11905)
• Guerra MO et al., Braz J Biol 2001 – toxicology of lapachol in rats: embryolethality
• Felício AC et al., Contraception 2002 – fetal growth in rats under lapachol
• BVL – substance list of the German federal government and federal states, category plants and plant parts (2014)
• EU Commission, Novel Food Catalogue (no entry for Tabebuia or lapacho, as of 10/2026)