Pau d'Arco is made from the inner bark of *Handroanthus impetiginosus*, a tree native to South America. The bark contains naphthoquinone compounds, particularly lapachol. Researchers have seen biological activity from these compounds in lab studies, but no solid evidence confirms those effects in people.
Traditional preparations generally aim for general wellness and immune upkeep. People usually drink it as a tea or take it as an extract, often cycling use with a few weeks on and a week off. Modern clinical research has not validated these traditional roles.
Safety matters a lot here. Lapachol and related compounds can stress the liver and cause toxicity, especially with high doses or continuous daily use. The bark also has anticoagulant properties that can interfere with blood thinning drugs. Pregnant or nursing women should avoid it completely.