Pau d'arco is the inner bark or heartwood of a tropical member of the bignonia family found in South America, including Brazil, Peru, and Argentina. Known in the herb trade as lapacho and taheebo, material sold as Pau d'arco in the American market may be from other Tabebuia species or from tropical trees in the verbena family.
In the Americas, Pau d'arco has a folk reputation as an anticancer, antibacterial, antiviral, and antifungal agent, especially for treating candida infections. Several Tabebuia species have long been used by South American indigenous groups as a cancer remedy. In Peru, Pau d'arco has been used to treat diabetes and as a blood purifier. It is often used in combination with other herbs. In the late 1960s, popular newspaper and magazine reports in Brazil led to widespread use in South America which prompted scientific research into its purported health benefits.
Pau d'arco has been studied for its antitumor, antiinflammatory, antibacterial, antifungal, and immunostimulant activities. Early results were promising. Immunostimulant action has been examined only in preliminary laboratory studies that did not involve living organisms. Research on anticancer activity was conducted in the late 1960s and early 1970s by the National Cancer Institute. Several chemicals known as quinones have been identified from the bark and heartwood; the primary component, lapachol, was admitted into clinical studies in its pure form but was withdrawn due to lack of substantial benefits and mild toxicity. Advocates of its use argue that the whole bark produces different effects, due to the combined action of dozens of chemicals, that cannot be expected from a single compound. Analyses of commercial products have found that many lack the known active constituents. Pau d'arco is, and is expected to remain, controversial. It is widely used by herbalists outside the United States to treat cancer; for viral infections such as colds, flu, and herpes; bacterial infections; fungal infections such as candida; inflammations of the nose and throat; and many other conditions.
Pau d'arco is available in a wide range of forms including powdered bark, capsules, tablets, tinctures, and extracts.
Reported side effects include nausea and gastrointestinal distress. The toxicity of T impetiginosa is considered relatively low. Other species have produced additional side effects. Pau d'arco should be approached cautiously: its anticancer activity is unconfirmed, identification of source species is often questionable, and it is surrounded by enough hype to make anyone skeptical.