Pau d'Arco (Lapacho)

• Almost no human safety data exist for pau d'arco bark tea or capsules. The only human trial of the bark in capsules was 12 women taking 1050 mg/day for 8 weeks with no comparison group. Nine finished, nine reported an adverse event (mostly mild, none an FDA serious adverse event), and the authors called tolerability moderate. That is too small to rule out rarer harms. Controlled trial ⁹
• Lapachol works against vitamin K like a blood thinner. In rat liver preparations lapachol strongly blocks two vitamin K enzymes in a way that resembles warfarin-type drugs, and the authors say this explains the anticoagulant activity seen earlier in rats and humans. A 2009 review lists interference with vitamin K as one of the most important interactions. MSK says pau d'arco may increase the effects of anticoagulant and antiplatelet drugs, with unknown clinical significance. How much lapachol reaches the blood from tea or capsules is not known. Laboratory research ^{14 7 11}
• Isolated lapachol and beta-lapachone are drug-level exposures, not the same as bark. Early human work with lapachol and a beta-lapachone analogue (ARQ 761, injected) reported side effects including nausea, vomiting, urine discoloration (MSK, lapachol), anaemia and low oxygen from possible methemoglobinaemia (ARQ 761). One mouse study found a bark extract with no detectable beta-lapachone. Do not read drug-trial toxicity as bark toxicity, or the reverse. Authoritative guidance ^{11 4 15}
• Product quality is unreliable. A 2009 review says material on international markets is of varying quality and composition, which makes claims hard to assess. A consumer site says potency varies between brands and batches. Lapachol and beta-lapachone are poorly water-soluble according to that site, so a tea may deliver little (secondary source, not traced to a primary study). Authoritative guidance ^{7 10}
• Avoid in pregnancy, breastfeeding and children unless a clinician says otherwise. No human pregnancy or breastfeeding data were found. MSK reports fetotoxic effects in rat studies; MedicineNet says there is not enough data and advises against use in pregnancy, breastfeeding and children. Authoritative guidance ^{11 10}

NIH LiverTox could not be opened (blocked by a browser check), so no liver rating is given. Neither the capsule trial abstract nor the other sources read describe liver injury: the trial reports only a few mild lab abnormalities. An earlier internal note mentioned a liver failure report from a patient-information site involving a mixed product; it was not independently verified and is not relied on. ⁹

How often. No frequency of liver injury was found.

Monitoring. No monitoring advice was found. Yellow skin or eyes, dark urine, or severe itching after taking any supplement is a reason to stop and seek care.

This is a safety connection. It is not evidence that Pau d'Arco (Lapacho) supports liver health.

Summary. No poisoning or overdose data for bark tea were found. Toxicity findings are for isolated compounds or animals.

Animal. MSK reports anaemia with large long-term lapachol doses, reduced seminal vesicle weight in male rats, fetotoxic effects and chromosomal abnormalities in mice. In tumour-bearing mice higher beta-lapachone doses produced toxic signs, though the bark extract used had no detectable beta-lapachone.

Human doses studied. Bark capsules 1050 mg/day for 8 weeks in 12 women (moderate tolerability); lapacho-based oral solution in 40 radiotherapy patients; injected ARQ 761 up to 390 mg/m2 (a drug, not bark).

High dose or long term signals. High amounts may cause serious bleeding and vomiting according to a consumer site (not traced to primary data); the claim on the same site that risk rises above 1.5 mg lapachol a day is likewise unverified.

Overdose response. No overdose data found. Seek urgent care for bleeding.

Genotoxicity. MSK reports chromosomal abnormalities in mice; no primary study read.

Toxic plant parts. No toxic plant part is named in the sources read. Products are made from inner bark; beta-lapachone was originally isolated from the heartwood (2021 review).

Identity and potency are the main concerns.

Variable quality and composition. A 2009 review says material on international markets is of varying quality and composition. A consumer site says supplements are not regulated like drugs so potency varies. ^{7 10}

Low lapachol content or lack of it. A secondary web source describes a 1987 Canadian analysis of 12 products in which only one contained lapachol, in tiny amounts. This is NOT verified from the original paper and is not relied on. In a mouse study, a bark extract had no detectable beta-lapachone. ¹⁵

Species confusion. Handroanthus impetiginosum, Tabebuia avellanedae and other Tabebuia species are sold as 'pau d'arco' or 'lapacho' and the 2020 review notes many synonyms; products may not be the same species. ¹⁸

• Black or bloody stools, blood in vomit, blood in urine, nosebleeds that will not stop, large unexplained bruises or any heavy bleeding.
• Blue or grey lips, breathlessness or unusual tiredness (possible low oxygen or anaemia, described with drug analogues).
• Repeated vomiting or being unable to keep fluids down.
• Yellow skin or eyes with dark urine.

Stop the supplement and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.