Pedra hume

Pedra Hume Caá (Myrcia spp.): A Comprehensive Reference

1. Identity and Botanical Classification

Nomenclature and Taxonomy

Pedra hume caá belongs to the family Myrtaceae, genus Myrcia, and encompasses the species salicifolia, uniflora, multiflora, and sphaerocarpa. Known synonyms include Aubmyrcia salicifolia and Myrcia multiflora. Common names include pedra hume caá, pedra-ume-caá, and insulina vegetal (insulin plant). The part used is the leaves. The name appears in the literature under several variant spellings: "pedra-hume-caá," "pedra-ume-caá," and occasionally "pedra hume de kaá." Both spellings refer to a curious trait: when the leaf is boiled in water, it "hardens like stone" — an Amazonian way of describing the strong tanning action of the plant's constituents.

In Brazil, the common name pedra hume caá refers to three species of Myrcia plants that are used interchangeably — Myrcia salicifolia, Myrcia uniflorus, and Myrcia sphaerocarpa. A broader listing of species historically associated with the same common name has been documented in the peer-reviewed literature: the species related to "pedra-hume-caá" are Myrcia sphaerocarpa, Myrcia citrifolia, Myrcia guianensis, Myrcia uniflora, Myrcia multiflora, Myrcia salicifolia, and Myrcia speciosa. It is unknown whether reports on pedra hume caá can be applied to other species in the Myrcia genus.

Morphology and Geographic Origin

Myrcia sphaerocarpa and its congeners are medium-sized shrubs that grow in drier regions of the Amazon and other parts of Brazil. They have small, green leaves and large, orange-red flowers, and they are members of the myrtle family — one of more than 150 species of Myrcia indigenous to tropical South America and the West Indies. Some Myrcia species also grow in other South American countries, including Bolivia, Peru, and Paraguay.

Common Forms and Preparations

Pedra hume caá is commercially available in several forms. Myrcia uniflora, popularly known as "pedra-hume-caá" in Brazil, is sold as dry extracts in capsules or as tinctures for the treatment of diabetes mellitus. Whole dried leaves are also sold for preparation as an infusion (leaf tea), the most traditional form of consumption. Powdered leaf is another widely available format used both in encapsulated supplements and for brewing as a tea.

2. Traditional and Historical Use

Indigenous and Amazonian Use

Pedra hume caá has been used by indigenous tribes in the rainforest for diabetes, diarrhea, and dysentery. The Taiwanos tribe (in northwest Amazonia) considers the leaves to be an astringent and uses them for persistent diarrhea. Ethnobotanical records note that the Taiwanos mixed dried leaves with farina; they are described as astringent and, if taken in excess, emetic.

The plants known as "pedra-hume-caá" or insulin plants have been used for the treatment of diabetes according to the empirical African and indigenous knowledge that influenced the formation of Brazilian culture. This reflects the multicultural convergence that shaped the Brazilian ethnobotanical tradition.

Brazilian Folk and Popular Medicine

Pedra hume caá has had a place in Brazilian traditional medicine for many years. Dr. G. L. Cruz, a leading Brazilian practitioner and herbalist, nicknamed it "vegetable insulin" in 1965. Dr. Cruz noted in his book Livro Verde das Plantas Medicinais e Industriais do Brasil that "one uses all parts of the plant in infusions, decoctions or extracts to combat diabetes." Specialists affirmed that regular use produces surprising results in the treatment of this ailment, as "in a short space of time the sugar disappears from the urine," giving rise to the name "vegetable insulin."

The plant remains a very popular natural remedy for diabetes throughout South America; the traditional use is a simple leaf tea with a pleasant, slightly sweet taste. Brazilian scientists have documented leaf extracts of pedra hume caá with hypoglycemic activity since 1929.

Myrcia multiflora, known as "pedra-hume-de caá," is used in folk medicine for the treatment of diabetes, diarrhea, enteritis, and hemorrhages. In the broader Brazilian ethnobotanical tradition, the plant has also been employed for dysentery, hypertension, mouth ulcers, hemorrhage, and as a topical astringent. Brazilian folk medicine utilizes the shrub Myrcia guianensis against various snake venom effects.

Historical Preparation Methods

Traditional preparation consistently involves aqueous extraction: leaves are prepared as infusions (steeping in hot or boiling water) or decoctions (simmered). Dr. Cruz documented that "one uses all parts of the plant in infusions, decoctions or extracts." The traditional dose in Brazilian folk medicine is a simple leaf tea consumed two to three times daily with meals.

3. Key Constituents and Active Compounds

Flavonoids and Flavanone Glucosides

The species are an important source of essential oils in which mono- and sesquiterpenes are predominant. The non-volatile compounds isolated from Myrcia are usually flavonoids, tannins, acetophenone derivatives, and triterpenes.

Following the earlier characterization of myrciacitrins I and II and myrciaphenones A and B, three new flavanone glucosides — myrciacitrins III, IV, and V — were isolated from the leaves of Brazilian Myrcia multiflora. Their structures were elucidated on the basis of physicochemical and chemical evidence, and myrciacitrins were found to show potent inhibitory activity on aldose reductase.

A 2016 study investigated α-glucosidase and α-amylase inhibitors from Myrcia species in comparison to acarbose, a pharmaceutical antidiabetic drug. α-glucosidase and α-amylase inhibitors from Myrcia spp. were characterized — the question posed was whether they represent "a stronger alternative to acarbose?" — published in the Journal of Pharmaceutical and Biomedical Analysis, January 2016.

The flavanone glucosides myrciacitrins I–II, the flavonol glucosides myricitrin, mearnsitrin, quercetin, desmanthin-1, and guaijaverin, and the acetophenone glucoside myrciaphenone B — all isolated from M. multiflora leaves — are among the key identified bioactive compounds. Among these, desmanthin-1 showed the most potent activity on aldose reductase.

The main plant chemicals documented in pedra hume caá include: beta-amyrin, catechin, desmanthin, gallic acid, ginkgoic acid, guaijaverin, mearnsitrin, myrciacitrin I–V, myrciaphenone A, myrciaphenone B, myricitrin, and quercitrin.

Acetophenone Derivatives

2′,4′,6′-Trihydroxyacetophenone (THAP) is isolated from Myrcia multiflora (Myrtaceae) and acts as a pancreatic lipase inhibitor to delay intestinal absorption of dietary fat, showing antiobesity and mixed lipid-lowering effects. This compound has been the subject of pharmacokinetic research using LC-MS/MS analytical methods.

Tannins

Ethnobotanical records note that "Pedra Huma-Caa contains a lot of tannin and its astringent action makes it a very useful plant." The high tannin content is responsible for the characteristic hardening effect when leaves are boiled, and tannins contribute to the observed astringent, antidiarrheal, and anti-hemorrhagic properties attributed to the plant in traditional medicine.

Essential Oils

The Myrcia species are an important source of essential oils, and most chemical studies on Myrcia describe the chemical composition of the essential oils, in which mono- and sesquiterpenes are predominant. Anti-inflammatory, antinociceptive, antioxidant, and antimicrobial activities have been described for Myrcia essential oils.

4. Established Mechanisms of Action

Aldose Reductase Inhibition

Flavonoid glucosides and acetophenone derivatives showed aldose reductase and α-glucosidase inhibition, and could explain the traditional use of Myrcia species to treat diabetes. Aldose reductase inhibitors (ARIs) are substances that act on nerve endings exposed to high blood sugar concentration to prevent some of the chemical imbalances that occur, thus protecting the nerves. Alpha-glucosidase inhibitors delay the digestion and subsequent absorption of sugar in the gastrointestinal tract.

The novel compounds in pedra hume caá that act upon aldose reductase and glucosidase are seen as at least partially responsible for the plant's blood sugar-balancing properties. Various ARIs (both synthetic and natural) are being studied by researchers; these compounds may be helpful in reducing or preventing some side effects of diabetes, including diabetic neuropathy and macular degeneration.

Alpha-Glucosidase Inhibition (Intestinal Glucose Absorption)

The methanol extract and ethyl acetate-soluble portion from M. multiflora leaves showed inhibitory activities on aldose reductase and α-glucosidase, on the increase of serum glucose level on sucrose-loaded rats, and on alloxan-induced diabetic mice. α-Glucosidase inhibition slows the post-meal rise in blood glucose by delaying carbohydrate digestion in the small intestine — the same mechanism exploited by pharmaceutical agents such as acarbose.

Insulin Signaling Pathway Activation

A 2014 study published in Evidence-Based Complementary and Alternative Medicine examined Myrcia bella leaf extract, a species related to pedra hume caá: Glycogen content and expression of proteins of the insulin signaling pathway were measured in liver. Treatment with 600 mg/kg reduced fasting blood glucose in diabetic mice by the 7th day, and also reduced water and food intake and increased hepatic glycogen. The investigators identified activity through the PI3K/Akt insulin signaling pathway.

Pancreatic Lipase Inhibition

Phloroacetophenone isolated from M. multiflora has hypolipidemic and antiobesity effects related to reduction of triglyceride intestinal absorption and pancreatic lipase activity inhibition. This mechanism parallels that of the pharmaceutical drug orlistat and provides a biochemical basis for traditional use claims related to weight and lipid management.

Antiglycation Activity

All extracts tested in a 2024 NMR-based study inhibited the formation of advanced glycation end products (AGEs) and showed free-radical-scavenging activity. Inhibition of AGE formation is considered a potentially important mechanism for reducing complications associated with chronic hyperglycemia.

5. Scientific Evidence by Area of Use

5.1 Diabetes / Hypoglycemic Activity

Human Clinical Evidence

Two clinical studies published in the 1990s demonstrated hypoglycemic activity and confirmed the traditional use of pedra hume caá for diabetes.

The most frequently cited clinical study is a 1990 double-blind, placebo-controlled trial: in a 1990 double-blind placebo clinical study with normal and Type II diabetic patients, pedra hume caá (3 g powdered leaf daily) demonstrated the ability to lower plasma insulin levels in the diabetic group. After ingestion of infusions of 3 g leaves/day of M. uniflora, no acute or chronic effects on plasma glucose levels or glycated hemoglobin were found in either the normal or diabetic group; however, plasma insulin levels in the diabetic group were lower after M. uniflora than after placebo. These findings suggest a modest effect on insulin metabolism but did not demonstrate reduction of blood glucose itself or glycated hemoglobin (HbA1c) in this cohort.

Limitations: The 1990 clinical study is small, dates from over three decades ago, and specific sample sizes and full methodological details are not widely available in the published secondary literature. Large human clinical trials are still lacking. No modern randomized controlled trials (RCTs) with adequate statistical power, standardized extracts, or rigorous glycemic endpoints have been published as of the most recent literature reviews.

Animal Evidence

In a 1993 study, 250 mg/kg of a leaf extract demonstrated the ability to reduce appetite and thirst, reduce urine volume, reduce urinary excretion of glucose and urea in diabetic rats. The extract also inhibited the intestinal absorption of glucose.

A 2023 study published in ScienceDirect investigated the cumulative effect of the dry leaf extract of M. multiflora in streptozotocin-induced diabetic mice: the M. multiflora leaf extract showed a hypoglycemic effect in diabetes-induced mice, inhibited lipid peroxidation in the liver of diabetic mice, and the dry extract exerted nephron- and hepatoprotective effects.

The methanol extract and ethyl acetate-soluble portion from M. multiflora leaves showed inhibitory activities on aldose reductase and α-glucosidase, on the increase of serum glucose level on sucrose-loaded rats and on alloxan-induced diabetic mice.

In Vitro Evidence

Chemical markers were identified in 15 commercial samples of pedra-ume-caá; only the extracts of M. multiflora and E. punicifolia inhibited α-glucosidase. All the extracts inhibited the formation of advanced glycation end products (AGEs) and showed free-radical-scavenging activity. A 2024 NMR and multivariate methods study published on PubMed thus revealed the chemical markers of matrices, differentiated materials marketed as pedra-ume-caá, and corroborated the potential of these species for treating diabetes.

Evidence strength — hypoglycemia: The preclinical (animal and in vitro) evidence is consistent and mechanistically plausible. The sole identified clinical trial (1990) was small and did not observe effects on blood glucose or HbA1c, only on plasma insulin levels. The overall human clinical evidence base is weak and preliminary. No regulatory body (EMA, WHO, ANVISA) has issued an approved therapeutic monograph for pedra hume caá as an antidiabetic agent.

5.2 Antidiarrheal / Gastrointestinal Activity

Hypoglycemic, anti-hemorrhagic, and antioxidant activities have been attributed to Myrcia extracts, while astringent and antidiarrheal effects are consistently reported in the ethnobotanical literature. The high tannin content of the leaves provides a plausible mechanistic basis for antidiarrheal effects: tannins precipitate proteins and reduce intestinal motility and secretion. Pedra hume caá has been used by indigenous tribes for diarrhea and dysentery; the Taiwanos tribe considers the leaves to be an astringent and uses them for persistent diarrhea.

Evidence strength — antidiarrheal: Evidence is entirely traditional and mechanistically supported by known tannin chemistry. No controlled clinical trials on this indication have been identified in the published literature.

5.3 Antiobesity and Hypolipidemic Activity

2′,4′,6′-Trihydroxyacetophenone (THAP), isolated from Myrcia multiflora, acts as a pancreatic lipase inhibitor to delay intestinal absorption of dietary fat, showing antiobesity and mixed lipid-lowering effects. In an acute preclinical assay, THAP caused greater total cholesterol (37%) and triglyceride (46%) serum level reduction than lovastatin (32% and 1%) or orlistat (26% and 34%), a HMG-CoA reductase inhibitor and pancreatic lipase inhibitor respectively.

Evidence strength — antiobesity/hypolipidemic: Evidence is preclinical only (animal and in vitro models). Despite impressive effect sizes in animal models, no human trials have been conducted on this indication. Results cannot be extrapolated to humans without further clinical investigation.

5.4 Antioxidant Activity

The most promising antioxidant activity, measured by DPPH scavenging activity, was found in M. fallax extracts (EC₅₀ 8.61 ± 0.22 µg·mL⁻¹), being slightly less active than quercetin and gallic acid (EC₅₀ 2.96 ± 0.17 and 2.03 ± 0.02 µg·mL⁻¹, respectively). Antioxidant activity across Myrcia species is well-documented in the phytochemical literature and is consistent with the high polyphenol and flavonoid content.

Evidence strength — antioxidant: Consistent in vitro evidence; no human clinical data evaluating antioxidant endpoints specifically for pedra hume caá.

5.5 Antimicrobial Activity

Anti-inflammatory, antinociceptive, antioxidant, and antimicrobial activities have been described for Myrcia essential oils. The best antimicrobial activity was observed for M. bella and M. fallax against Escherichia coli (300 and 250 µg·mL⁻¹, respectively).

Evidence strength — antimicrobial: Preliminary in vitro evidence only. No clinical trials available.

5.6 Anti-Hemorrhagic Activity

Brazilian folk medicine utilizes the shrub Myrcia guianensis against various snake venom effects. The aqueous extract and the aqueous residue at 1:1 (w/w) of the leaves of M. guianensis completely inhibited the hemorrhagic effect produced by intradermic injections of crude venom of the snake Bothrops jararaca in Swiss mice; the ethyl acetate extract at 1:3 (w/w) inhibited 90.7%. It is suggested that the antihemorrhagic activity of the aqueous residue is mainly due to protein precipitation, as shown by electrophoresis.

Evidence strength — anti-hemorrhagic: Preclinical (murine) in vivo evidence only, with a plausible tannin-mediated mechanism. No human clinical evidence.

6. Body Systems and Health Areas Associated with Pedra Hume Caá

• Metabolic / Endocrine: Blood glucose regulation, insulin metabolism, type 2 diabetes management — the primary area of scientific inquiry and traditional use.
• Gastrointestinal: Antidiarrheal, antidysenteric, astringent effects on the gut; traditional use for diarrhea, dysentery, and enteritis.
• Cardiovascular / Lipid Metabolism: Hypolipidemic and antiobesity activity linked to THAP-mediated pancreatic lipase inhibition; traditional use for hypertension.
• Antioxidant / Cellular Protection: Free-radical scavenging and inhibition of advanced glycation end-product (AGE) formation.
• Anti-hemorrhagic: Traditional and preclinical use for hemorrhage, wound care, and potentially snakebite-related hemorrhage.
• Antimicrobial / Oral Health: Astringent and antibacterial properties applied topically to mouth ulcers and wounds.
• Thyroid: Identified as an area of safety concern (see Section 8).

7. Dosage Forms and Reported Dosages

Reported dosages in the available literature come primarily from traditional use accounts and one identified clinical study; no standardized therapeutic dose has been established by any regulatory or pharmacopeial authority.

• Leaf infusion (tea): The 1990 clinical trial used 3 g of powdered leaf per day as an infusion in diabetic and normal patients.
• Traditional tea preparation: Traditionally taken in 1-cup amounts, 2–3 times daily.
• Animal study dose: In a 1993 animal study, 250 mg/kg of a leaf extract was administered to diabetic rats.
• Animal study dose (PI3K/Akt study): Treatment with 600 mg/kg reduced fasting blood glucose in diabetic mice by day 7.
• Encapsulated/powdered leaf: M. uniflora is sold as a dry extract in capsules at commercially variable doses.

The animal-model doses are cited for scientific context only; they cannot be directly translated to human dosing recommendations without clinical pharmacokinetic data.

8. Safety Considerations and Interactions

Thyroid Peroxidase Inhibition (Hypothyroidism Risk)

The most substantiated safety concern identified in the peer-reviewed literature relates to thyroid function. Thyroid peroxidase (TPO), the key enzyme in thyroid hormone biosynthesis, is inhibited by dietary flavonoids, and high consumption of plants containing inhibitory flavonoids may affect thyroid function and lead to hypothyroidism. In vitro work confirmed that the aqueous partition of the methanolic extract of M. uniflora is able to inhibit TPO activity, and two known flavonoids were isolated from plant extracts: mearnsitrin and myricitrin. The degree of TPO inhibition was very high, with a 50% inhibition of the original TPO activity (IC₅₀) obtained at 1.97 μM mearnsitrin and at 2.88 μM myricitrin. These results suggest that indiscriminate consumption of M. uniflora pharmaceutical products, allied to nutritional deficiency of iodine, might contribute to the development of hypothyroidism.

Myrcia might decrease the production of thyroid hormone, which might worsen symptoms in individuals with existing underactive thyroid (hypothyroidism). This finding is based on in vitro data; the clinical significance of this inhibition at typical consumed doses has not been formally established, but the mechanism is biologically plausible and the effect magnitudes are notable.

Hypoglycemia Risk with Antidiabetic Medications

Pedra hume caá has been documented to lower blood sugar levels in animal and human studies. Additive hypoglycemic effects are therefore a theoretical concern in individuals taking pharmaceutical antidiabetic drugs (e.g., insulin, sulfonylureas, metformin). This interaction has not been formally evaluated in clinical pharmacokinetic studies, but the mechanism is consistent with the documented pharmacology.

Emetic Properties at High Doses

Ethnobotanical records note that the dried leaves are described as astringent and, if taken in excess, emetic. This traditional warning is consistent with the high tannin content, which at large doses can irritate the gastrointestinal tract.

Species Adulteration and Commercial Identity

It is unknown whether reports on pedra hume caá can be applied to other species in the Myrcia genus. Chemical marker studies have identified markers in 15 commercial samples of pedra-ume-caá, highlighting that the commercial market contains heterogeneous species. Only the extracts of M. multiflora and E. punicifolia inhibited α-glucosidase among tested commercial samples, suggesting that not all products sold under this name share the same pharmacological profile. The lack of species standardization in commercial preparations is a significant concern for both efficacy and safety.

Pregnancy and Lactation

There is not enough reliable information to know whether Myrcia is safe to use when pregnant or breast-feeding.

Overall Safety Evidence Status

No formal toxicology studies establishing a no-observed-adverse-effect level (NOAEL) or acceptable daily intake (ADI) for pedra hume caá preparations in humans have been published in the accessible peer-reviewed literature. In the 2024 NMR/chemometrics study, the tested extracts did not present cytotoxicity in the cell-based models used, which provides limited reassurance at the tested concentrations but does not substitute for comprehensive safety evaluation.

References

• Cascaes M, et al. "Constituents and Pharmacological Activities of Myrcia (Myrtaceae): A Review of an Aromatic and Medicinal Group of Plants." Int. J. Mol. Sci. 2015; 16(10): 23881–904. PMC4632730
• Cascaes M, et al. PubMed abstract — Constituents and Pharmacological Activities of Myrcia (Myrtaceae). PMID: 26473832
• Vareda P, et al. "Myrcia bella Leaf Extract Presents Hypoglycemic Activity via PI3k/Akt Insulin Signaling Pathway." Evid. Based Complement. Alternat. Med. 2014; 2014: 543606. PMC4020406
• Ferreira AC, et al. "Inhibition of Thyroid Peroxidase by Myrcia uniflora Flavonoids." Chem. Res. Toxicol. 2006; 19(3): 351–55.
• Ferreira AC, et al. PubMed — Inhibition of thyroid peroxidase by Myrcia uniflora flavonoids. PMID: 16544938
• Matsuda H, et al. "Antidiabetic principles of natural medicines. V. Aldose reductase inhibitors from Myrcia multiflora DC. (2): Structures of myrciacitrins III, IV, and V." PMID: 11911215
• NMR and multivariate methods: Identification of chemical markers in extracts of pedra-ume-caá and their antiglycation, antioxidant, and enzymatic inhibition activities. PubMed PMID: 38191126
• Hypoglycemic effect of the dry leaf extract of Myrcia multiflora in streptozotocin-induced diabetic mice. ScienceDirect, 2023.
• Antioxidative, Antiproliferative and Antimicrobial Activities of Phenolic Compounds from Three Myrcia Species. PMC6100318
• Development and Validation of an LC-MS/MS Assay to Quantitate 2′,4′,6′-Trihydroxyacetophenone in Rat and Dog Plasma. PMC7583961
• Wikipedia — Myrcia sphaerocarpa
• Taylor L. "Pedra Hume Caa" — Tropical Plant Database, Rain-Tree.com (citing published clinical and phytochemical research).
• WebMD Natural Medicines — Myrcia (ingredient monograph)
• RxList — Myrcia: Health Benefits, Side Effects, Uses, Dose & Precautions
• Ferreira EA, et al. "The 2′,4′,6′-Trihydroxyacetophenone Isolated from Myrcia multiflora Has Antiobesity and Mixed Hypolipidemic Effects." Planta Med. 2011; 77(14): 1569–74.
• Sousa LA, et al. "The effect of the aqueous extract of Myrcia guianensis and its fractions against the hemorrhagic activity of Bothrops jararaca venom." J. Medicinal Plants Res. 2013; 7: 3139–3146.
• ResearchGate — Constituents and Pharmacological Activities of Myrcia (Myrtaceae): A Review (full text PDF)