Traditionally used for
- Cough & breathing
- Colds & fever
- Urinary & fluids
- Nerves & recovery
☯ TCM Properties
Dislodges Phlegm, cools Heat, extinguishes Wind, calms fright, settles convulsions, calms asthma and resolves toxicity; Clears Heat, Resolves toxicity, calms wheezing, transforms Phlegm, resolves swelling and softens hardness
Traditional Chinese Uses
Hou Zao ("monkey bezoar") is a calcareous concretion formed in the gallbladder or gut of macaques such as Macaca mulatta (Calculus Macacae Mulattae). Bitter and salty with a cold nature, entering the Heart, Lung, Liver and Bladder channels, it was traditionally used to dislodge and cool Phlegm-Heat, extinguish Wind and settle fright and convulsions, and to clear Heat, resolve toxicity and soften hardness. Classic indications are high fever with Phlegm veiling the Heart orifices, childhood fright-wind and convulsions, cough and wheezing from Phlegm-Heat, and scrofula and phlegm nodules; it functions analogously to Niu Huang and is given in tiny powdered doses within pediatric and Phlegm-Heat formulas.
Because it can only be obtained by killing the animal, Hou Zao is a restricted, conservation-sensitive substance; macaques are legally protected under wildlife and CITES controls. This entry is historical: sourcing is discouraged and cow gallstone (Niu Huang) or synthetic bezoar substitutes are used instead.
Relationships
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Botanical Description
Hou Zao, "monkey bezoar," is a calcareous concretion that occasionally forms in the gallbladder, intestines, or bladder of macaques (Macaca mulatta and related Macaca species). The substance appears as an ovoid to irregularly shaped, hard, brown to grey-brown stone, 2-6 cm across, with a smooth or slightly granular surface, a layered cross-section, and a faintly bitter, slightly salty taste. It is rarely encountered and was historically valued as an exceptional substitute or analogue for Niu Huang (cattle bezoar) in classical TCM, used in small doses to clear heat, resolve toxins, transform phlegm, open the orifices, calm the spirit, and arrest convulsions in high-fever conditions, childhood epilepsy, and certain forms of stroke with internal heat. Modern supply is extremely limited and concerns over the source species' welfare and CITES Appendix II listing of macaques have largely confined Hou Zao to historical and rare ethnopharmacological references.
Active Constituents
Ellagic acid
Ellagitannin-derived polyphenolConcentration: 72.72 to 89.41 percent of the medicinal portion across 13 batches of raw material, measured by validated UPLC-qTOF-MS and UPLC-DAD methods
This single polyphenol is most of the drug. Its presence makes chemical sense once the true origin is understood: the commercial article forms in the caecum around Acacia nilotica seeds, and acacia is rich in hydrolysable tannins that yield ellagic acid. Ellagic acid itself is very poorly absorbed, so whatever systemic activity the drug has depends on gut microbial conversion rather than on the parent compound.
Urolithins (seven gut microbial metabolites of ellagic acid)
Dibenzo[b,d]pyran-6-one metabolitesConcentration: 2.14 to 5.13 percent of the medicinal portion as total urolithins; seven individual urolithins identified exclusively in the medicinal portion and absent from the non-medicinal portion and from 50 co-formulated Chinese medicinals
These are the compounds that distinguish the drug analytically. They are gut microbial metabolites of ellagic acid, and their presence preformed in the bezoar makes this the only known Chinese medicinal that supplies urolithins directly rather than requiring the patient's own microbiota to make them. Because they are unique to the medicinal portion, they are also the practical authentication markers.
Free and bound amino acids
Amino acidsConcentration: 1.19 to 5.91 percent of the medicinal portion
A minor fraction. Together with ellagic acid, the urolithins and the ash, amino acids account for more than 90 percent of the mass of the medicinal portion, which means the drug is chemically far simpler than its price and reputation suggest.
Inorganic ash residue
Inorganic mineral residueConcentration: Total ash about 2.09 percent
The mineral fraction of the concretion. It is small, which distinguishes this bezoar from the mineral-dominated calculi of other species and is consistent with a mass built from plant tannin rather than from precipitated salts.
⚠ Drug Interactions
Goat bezoar (Caprae Calculus, from Capra aegagrus hircus) supplied as macaque bezoar
Zhong Hua Ben Cao describes Houzao as the gastrointestinal concretion of Macaca mulatta or Macaca speciosa, with production regions given as India, the Malay Peninsula and the Malay Archipelago. Field investigation published in 2018, including on-site dissection of goats in Telangana, India, established that so-called Indian Houzao, which accounts for over 95 percent of actual market utilisation, is a caecal bezoar of domestic Indian goats formed over roughly 120 days around Acacia nilotica seeds. Genuine macaque-derived material is a negligible and unstable share of supply. The 2025 chemical characterisation was accordingly performed on goat bezoar and titles it as such; its ellagic acid and urolithin profile is that of a tannin-rich plant seed matrix, not of a primate. Nothing in this database's chemistry for Hou Zao is chemistry of Macaca mulatta.
Clinical note: Prescribe and document this drug as goat bezoar unless the supplier can substantiate a macaque origin, which is very unlikely. Tell any patient who objects to animal-derived medicines that this is one, and that the species is caprine. If a supplier does claim macaque origin, that raises the CITES question below rather than reassuring you.
Genuinely macaque-derived bezoar and CITES-controlled trade
All primate species are CITES-listed, either in Appendix II, where commercial trade is regulated and requires an export permit, or in Appendix I, which generally precludes commercial trade. Macaca mulatta falls under the Appendix II listing that covers primates not separately placed in Appendix I. A derivative such as a bezoar taken from the animal is a specimen for CITES purposes, so genuine macaque Houzao crossing a border requires permits. This is a legal position verified from the CITES framework and peer-reviewed primate trade literature; the CITES Species Plus database should be checked for the current appendix and for any national measure before any import, because macaque listings have been the subject of recent proposals.
Clinical note: Do not import or accept material represented as macaque bezoar without documentation. In practice the commercial article is caprine and outside CITES, which is the more likely reason a shipment clears rather than any permit having been granted.
Commercial proprietary Houzao products (paediatric cough preparations)
When the validated quantitative method for ellagic acid and urolithins was applied to 38 batches of commercial products, goat bezoar may have been absent from 20 of them, while all the raw goat bezoar powder samples tested were authentic. The failure is therefore at the manufactured-product stage rather than in the raw drug supply chain.
Clinical note: Prefer authenticated raw powder over a proprietary product. If a proprietary preparation is used, ask the manufacturer for ellagic acid and urolithin assay data rather than relying on the ingredient list.
Broad-spectrum antibiotics and other gut-microbiota-disrupting therapy
The medicinal portion is 73 to 89 percent ellagic acid, a polyphenol with very poor oral bioavailability whose systemic effects are generally mediated by gut microbial conversion to urolithins. The bezoar does supply some urolithins ready formed, but they are only 2 to 5 percent of the mass. Suppressing the colonic microbiota would be expected to blunt conversion of the remainder. No study of this specific interaction exists; the reasoning follows from the composition established in 2025.
Clinical note: No action is required, but do not read a poor response during or shortly after a course of antibiotics as evidence that the drug does not work for that patient.
Evidence Tier
Limited evidence · 1 studyRecorded studies by study design, strongest design at the top. This is a study-design tier only, not a GRADE rating: it does not weigh risk of bias, consistency or precision.
Systematic review / meta-analysis
0
Randomized controlled trial
0
Other clinical trial
0
Observational / case report
0
In vitro / animal
1
1 verified · 0 unverified
Other / unclassified
0
Verified: design read from PubMed for a DOI that resolves to the cited paper Unverified: taken from the study's recorded description
Clinical Studies
Quality Analysis of Raw Material and Products of Goat Bezoar (Houzao), a Mysterious Traditional Medicine
Analytical characterisation of the drug by UPLC-qTOF-MS with validated UPLC-DAD quantitation, applied to 13 batches of raw material and 38 batches of commercial products. Eight characteristic markers, ellagic acid and seven of its gut microbial urolithin metabolites, were found only in the medicinal portion and not in the non-medicinal portion or in 50 co-formulated Chinese medicinals. Ellagic acid at 72.72 to 89.41 percent, total urolithins at 2.14 to 5.13 percent, amino acids at 1.19 to 5.91 percent and total ash at 2.09 percent together account for over 90 percent of the medicinal portion. The commercial survey found goat bezoar may be absent from 20 of the 38 products while all raw powders were authentic. This is analytical and quality-control work, not a clinical trial; no efficacy claim follows from it.
Historical Texts
Yaowu Chuchan Bian (Analysis of the Production Regions of Medicinals), Chen Renshan
Republican China, 1930Zhong Hua Ben Cao (Chinese Materia Medica)
Modern compendium, 1999References
This information is for educational purposes only and is not intended to replace professional medical advice. Always consult a qualified healthcare provider before using any herbal remedy, especially if you are pregnant, nursing, or taking medications.
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