Lagerstroemin

Synopsis

Lagerstroemin: A Comprehensive Reference Article

1. Identity: Botanical Origin, Chemical Classification, and Common Names

1.1 Botanical Source

Lagerstroemin is an ellagitannin isolated from the leaves of Lagerstroemia speciosa (L.) Pers. (family Lythraceae). This tree is widely known by its Tagalog common name, banaba, and is also called crepe myrtle, giant crape myrtle, pride of India, queen's flower, and queen's crepe myrtle in the English-language literature. It is grown in Southeast Asia, China, India, Bangladesh, and the Philippines, and its native range extends through the western ghats of India, including Belgaum, north and south Kanara, Malabar, and Travancore, as well as Assam and West Bengal.

L. speciosa, commonly planted as an ornamental along roadsides and in gardens and parks, can grow up to 20 m in height. The leaves are obovate, simple, and opposite. The flowers are pink to purple when in bloom and give way to oval, nut-like fruits. The bark of the tree peels off in flakes.

1.2 Chemical Classification and Structural Identity

Lagerstroemin belongs to the class of hydrolyzable tannins, specifically the ellagitannin subclass. The structure of lagerstroemin, a new hydrolyzable tannin, was elucidated in early work on Lagerstroemia flos-reginae Retz. (Lythraceae). Its structure, as with related ellagitannins from the same species, was determined using proton and carbon-13 nuclear magnetic resonance spectroscopy and involved characterization of the glucopyranose core and valoneoyl group orientation. Its name is derived directly from the genus Lagerstroemia, reflecting its primary botanical source.

Seven ellagitannins — lagerstroemin (1), flosin B (2), stachyurin (3), casuarinin (4), casuariin (5), epipunicacortein A (6), and 2,3-(S)-hexahydroxydiphenoyl-α/β-D-glucose (7) — together with one ellagic acid sulfate, ellagic acid, and four methyl ellagic acid derivatives were identified by bioassay-directed isolation from the leaves of Lagerstroemia speciosa (L.) Pers. Lagerstroemin is thus one member of a larger ellagitannin complex that contributes to the pharmacological profile of the plant.

The extracts of L. speciosa contain abundant tannins (40%), with six ellagitannins including lagerstroemin, flosin B, stachyurin, casuarinin, casuariin, and 2,3-(S)-hexahydroxydiphenoyl-glucose constituting a major fraction of this tannin content.

1.3 Co-occurring Bioactive Compounds

Lagerstroemin does not occur in isolation in the plant. Other known compounds, including corosolic acid, gallic acid, 4-hydroxybenzoic acid, 3-O-methylprotocatechuic acid, caffeic acid, p-coumaric acid, kaempferol, quercetin, and isoquercitrin, were also isolated from the same plant. The triterpene acid corosolic acid is frequently discussed alongside lagerstroemin as a major contributor to the plant's antidiabetic activity, and their relative contributions continue to be a topic of investigation.

1.4 Dosage Forms and Preparations

Lagerstroemin is not typically marketed or studied as an isolated purified compound in human use; rather, it is encountered as a constituent of whole leaf extracts and standardized preparations of L. speciosa. Common applications of L. speciosa products include tea bags, dried herbs, ready-to-drink preparations, juice, beverages, as well as capsules and tablets for dietary supplements. Its leaf extracts have been developed into functional food products such as emulsions, soft gel capsules, and hard capsules, used in candies, bread, pastries, beverages, and other food products. Because most human studies use standardized whole-leaf extracts (often standardized to corosolic acid content) rather than isolated lagerstroemin, dosing data specific to purified lagerstroemin is not available from human clinical sources.

2. Traditional and Historical Use

2.1 Philippine Folk Medicine

The leaves of Lagerstroemia speciosa, a Southeast Asian tree more commonly known as banaba, have been traditionally consumed in various forms by Filipinos for the treatment of diabetes and kidney-related diseases. Banaba extracts have been used for many years in folk medicine to treat diabetes, with the first published research study being reported in 1940. Banabá herb is one of the 69 herbal plants promoted by the Philippine Department of Health (DOH).

Folkloric use of banaba leaf decoctions for diuretic and purgative purposes and of the bark and root parts for stomach ailments has also been recorded. The leaf decoction — produced by boiling dried leaves in water — has been the most prevalent traditional preparation for managing blood sugar levels.

2.2 Use Across Southeast and South Asia

Plants of the genus Lagerstroemia have been extensively utilized in traditional herbal medicine across various Asian countries, notably China, India, the Philippines, and Malaysia. The genus, known for its exquisite flowers and prolonged flowering period, is commonly employed in traditional medicinal systems across Asian countries, where it has been consumed as tea or employed to address ailments such as diabetes, urinary disorders, coughs, fevers, inflammation, pain, and anesthesia.

In Vietnam, the plant's young leaves are consumed as vegetables, and its old leaves and mature fruit are used in traditional medicine for reducing glucose in blood. L. speciosa was also listed among the 170 medicinal plants registered by the Ministry of Public Health in Thailand.

2.3 Ayurvedic and South Asian Tradition

Lagerstroemia speciosa is one of the most important medicinal plants mentioned in the Ayurvedic classic Bhavaprakash Nighantu, having an anti-diabetic action; modern scientific studies have also found that this plant has a potent hypoglycemic effect. Historical literature reveals that the earliest description of Madhumeha (diabetes mellitus) is found in Vedic literature of India, and the hypoglycemic effect of Lagerstroemia speciosa (L.) Pers. has been referenced in the old writings of Ayurveda (Bhavaprakash Nighantu).

2.4 Japan and East Asia

The leaves of banabá and other parts are used widely in the Philippines, Taiwan, and Japan as a tea preparation. Banabamin, a tablet containing extract from banaba tea, has been marketed in Japan as a food to promote health. It has become a popular health beverage in East Asia and the United States.

3. Key Constituents and Active Compounds

3.1 Lagerstroemin's Place in the Phytochemical Profile

At least 364 biological compounds have been identified from Lagerstroemia extracts, encompassing various types such as terpenes, flavonoids, phenolic acids, alkaloids, and phenylpropanoids. Among these, lagerstroemin is distinguished as one of the ellagitannins most specifically linked to insulin receptor activation and glucose transport stimulation.

Steroids, terpenoids, glycosides, phenolic compounds, amino acids, saponins, starch, alkaloids, carbohydrates, organic acids, flavonoids, reducing sugars, tannins, and many other active metabolites have been found in Lagerstroemia speciosa leaf and fruit, according to phytochemical analyses.

3.2 Structural Characterization of Lagerstroemin

Glucose transport enhancers were searched for in Lagerstroemia speciosa, a Philippine local herbal medicine used for diabetes mellitus; bioassay-guided fractionation of the aqueous acetone extract of the leaves afforded three active ellagitannins — lagerstroemin, flosin B, and reginin A — identified by NMR and optical rotation. The ellagitannin class is defined by the esterification of gallic acid dimer units (hexahydroxydiphenic acid, which lactonizes to ellagic acid upon hydrolysis) with a polyol core, typically glucose.

3.3 Valoneaic Acid Relationship

Valoneaic acid exists as a structural part of the polyphenols which, like flosin A, reginin A, and lagerstroemin, are characteristic constituents of banaba. The structural relationship of lagerstroemin to valoneaic acid-bearing tannins is thus a defining chemical feature of this class of banaba ellagitannins.

4. Mechanisms of Action

4.1 Insulin Receptor Activation

The most extensively characterized mechanism of lagerstroemin is its direct activation of the insulin receptor (IR). Lagerstroemin, an ellagitannin isolated from the leaves of Lagerstroemia speciosa (L.) Pers. (Lythraceae), was examined for its biological activities. In rat adipocytes, the compound increased the rate of glucose uptake and decreased the isoproterenol-induced glycerol release. In Chinese hamster ovary cells expressing human insulin receptors, it increased Erk activity. These insulin-like actions were accompanied by the increased tyrosine-phosphorylation of the beta-subunit of the insulin receptors. Tryptic digestion of the extracellular sites of the insulin receptors markedly increased the effective concentrations of insulin without changing those of lagerstroemin.

The mechanistic implication of this tryptic digestion experiment is significant: tryptic digestion of the extracellular sites of the insulin receptors markedly increased the effective concentrations of insulin without changing those of lagerstroemin, indicating that lagerstroemin was considered to cause its insulin-like actions by a mechanism different from that employed by insulin itself. In other words, lagerstroemin does not compete at the conventional insulin binding site; rather, it appears to activate the receptor through a distinct allosteric or extracellular mechanism.

A possible mechanism of the antidiabetic effect of tannins such as lagerstroemin through activation of insulin receptors was also suggested from studies on Chinese hamster ovary cells expressing human insulin receptors, where an increase in mitogen-activated protein kinases (MAPK) activity coupled with increased tyrosine-phosphorylation of the β-subunit of the insulin receptors were shown to be induced by the compound.

4.2 Glucose Transport Stimulation

After HPLC purification, ellagitannins were identified in the water extract of banaba as the activators of glucose transport in fat cells with a glucose uptake assay; one of the most potent ellagitannins was named "Lagerstroemin." In the ellagitannin study, lagerstroemin exhibits glucose transport stimulation at 40 μM with an EC50 of 80 μM. For context, α- and β-PGG (penta-O-galloyl-glucopyranose) exhibit activity at a concentration as low as 10 μM with EC50 of 17 and 18 μM; in other words, α- and β-PGG are about five times more potent than lagerstroemin in stimulating glucose transport. This comparative data situates lagerstroemin as an active, but not the most potent, of the tannin-type glucose transport stimulators in banaba leaf.

4.3 Anti-Lipolytic Activity

Beyond glucose uptake, lagerstroemin also has demonstrated anti-lipolytic activity. In rat adipocytes, the compound increased the rate of glucose uptake and decreased the isoproterenol-induced glycerol release; in Chinese hamster ovary cells expressing human insulin receptors, it increased Erk activity. Decreased isoproterenol-induced glycerol release reflects inhibition of lipolysis — the breakdown of triglycerides to fatty acids and glycerol — which is an insulin-mimetic effect.

4.4 Antioxidant and Free Radical Scavenging

The antioxidant properties of L. speciosa tea, particularly when subjected to freeze-drying during the drying process, were significantly enhanced, possibly attributed to ellagitannins such as lagerstroemin, flosin, and reginin. Banaba extract showed strong antioxidative activity in a linoleic acid autoxidation system; banaba extract was found to have a potent radical scavenging action on DPPH radicals and superoxide radicals generated by a hypoxanthine/xanthine oxidase system. In vitro lipid peroxidation of rat liver homogenate induced by tert-butyl hydroperoxide was inhibited by the addition of banaba extract in a dose-dependent manner. From these results, banaba extract was demonstrated to be useful as an antioxidant or free radical scavenger to protect biological systems against oxidative stress. While these findings are attributed to the whole extract rather than isolated lagerstroemin specifically, the ellagitannin fraction — of which lagerstroemin is a primary component — is implicated in this activity.

4.5 Hypoglycemia via Multiple Pathways

While corosolic acid was traditionally considered the active component for glucose reduction in Lagerstroemia plants, multiple studies have suggested that the hypoglycemic activity results from the combined effects of various chemical components, including corosolic acid, ursolic acid, PGG, lagerstroemin, flosin B, reginin A, asiatic acid, valoneaic acid dilactone, and others. This multi-compound synergy is an important aspect of understanding lagerstroemin's functional context within banaba-based preparations.

The beneficial effects of banaba and corosolic acid with respect to various aspects of glucose and lipid metabolism appear to involve multiple mechanisms, including enhanced cellular uptake of glucose, impaired hydrolysis of sucrose and starches, decreased gluconeogenesis, and the regulation of lipid metabolism; these effects may be mediated by PPAR and other signal transduction factors.

5. Scientific Evidence by Area of Use

5.1 Antidiabetic Activity (Blood Glucose Regulation)

In Vitro Evidence

Glucose transport enhancers were searched for in Lagerstroemia speciosa, a Philippine local herbal medicine used for diabetes mellitus; bioassay-guided fractionation of the aqueous acetone extract of the leaves afforded three active ellagitannins — lagerstroemin, flosin B, and reginin A — identified by NMR and optical rotation. These compounds increased glucose uptake of rat adipocytes and could be responsible for lowering blood glucose levels.

A study reported the activation of the insulin receptor (IR) by lagerstroemin; in this study, lagerstroemin was able to induce phosphorylation of the β-subunit of IR at 150 μM, but the mechanism responsible for IR activation was distinct from that of insulin.

The hot water extract and the methanol eluent of leaves were shown to stimulate glucose uptake in 3T3-L1 adipocytes with an induction time and a dose-dependent response similar to those of insulin.

Animal Evidence

The hypoglycemic effects of Lagerstroemia speciosa, known as banaba in the Philippines, were studied using hereditary diabetic mice (Type II, KK-AY/Ta Jcl). The mice were fed a test diet containing 5% of the hot-water extract from banaba leaves for a feeding period of 5 weeks. The elevation of blood plasma glucose level in non-insulin dependent diabetic mice fed the control diet were almost entirely suppressed by addition of either the hot-water extract or the methanol eluent fraction.

Ellagitannins including lagerstroemin, flosin B, and reginin A increased glucose uptake of rat adipocytes. Another report evaluated a deterioration of this insulin-like principle from the plant, demonstrating that 20 g of old leaves or fruits dried 1–2 weeks had hypoglycemic activity equivalent to 6 to 7.7 units of insulin — it differs from insulin in that it is thermostable and lowers blood sugar upon oral administration instead of by injection.

Human / Clinical Evidence

Human studies of lagerstroemin as an isolated compound are not available; clinical trials have used whole banaba leaf extracts in which lagerstroemin is one among several bioactive constituents. The evidence at the human level is therefore indirect.

The antidiabetic activity of an extract from the leaves of Lagerstroemia speciosa standardized to 1% corosolic acid (Glucosol) was demonstrated in a randomized clinical trial involving Type II diabetics. Subjects received a daily oral dose of Glucosol, and blood glucose levels were measured; Glucosol at daily dosages of 32 and 48 mg for 2 weeks showed a significant reduction in blood glucose levels. Glucosol in a soft gel capsule formulation showed a 30% decrease in blood glucose levels compared to a 20% drop seen with dry-powder filled hard gelatin capsule formulation (P<0.001), suggesting that the soft gel formulation has better bioavailability.

A proprietary product called Banabamin in tablet form containing an aqueous extract of banaba was used in a human clinical study; this product also contained extracts of green tea, green coffee, and Garcinia. Twenty-four human subjects with mild type 2 diabetes were given three tablets three times daily; a 13.5% average decrease in blood glucose levels was reported, and no adverse effects were observed, though the constituents in the product responsible for the antidiabetic effect were not determined.

Ikeda et al. also conducted a 1-year open label safety and efficacy study on 15 subjects, administering 100 mg tablets daily of a water soluble banaba extract; the extract was not standardized, and the constituent(s) responsible for the antidiabetic effects was not determined.

A randomized, double-blind, placebo-controlled clinical trial was carried out to evaluate the effect of banaba on metabolic syndrome, insulin sensitivity, and insulin secretion in 24 patients with diagnosed metabolic syndrome according to the International Diabetes Federation criteria; twelve patients received banaba (500 mg) twice a day, before breakfast and dinner, for 12 weeks, and the remaining 12 patients received placebo at the same dosage.

Banaba leaf preparations have been used in Philippine folk medicine for the treatment of diabetes; however, reviews of medical literature on the effects of banaba in diabetes have identified few quality clinical trials and some open-label or small studies. Clinical trial data are lacking to recommend banaba for any indication.

Evidence strength assessment: The in vitro and animal evidence for lagerstroemin's antidiabetic mechanisms is robust and consistent across multiple studies. Human clinical evidence is limited to small, often open-label, or combination-product trials that preclude attribution of effects to lagerstroemin specifically. No large, well-controlled human trials have isolated lagerstroemin's contribution.

5.2 Anti-Obesity / Adipogenesis Inhibition

Lagertannins from L. speciosa, including lagerstroemin, stimulate glucose transport and have demonstrated adipocyte differentiation inhibitory activity in 3T3-L1 cells, which may be relevant to weight management.

Realizing the potential problems associated with cell line selection and assay methods, researchers acknowledged that corosolic acid could not represent the whole activity of banaba extract and switched their cell model from the original tumor cells to a natural cell target of insulin, adipocytes, in order to allow for the isolation and identification of more active compounds using improved methodology. This methodological shift led directly to the identification of lagerstroemin and its insulin-mimetic properties in the adipocyte model.

Both α- and β-PGG possess the adipogenesis inhibitory activity exhibited by the banaba extract and by the tannin-rich fraction. While PGG and lagerstroemin share the glucose-transport stimulatory property, the anti-adipogenesis activity has been more clearly attributed to the gallotannin PGG in comparative in vitro work.

Evidence strength assessment: Evidence for anti-obesity effects involving lagerstroemin remains at the level of in vitro cell culture, with supporting but non-specific animal data on whole extracts. No human clinical trials have examined lagerstroemin's anti-obesity effects as an isolated compound.

5.3 Antioxidant Activity

When investigating the antioxidant properties of various traditional herbal teas, it was found that L. speciosa tea exhibited superior antioxidant properties compared to green tea, surpassing oolong tea, black tea, and moringa (Moringa oleifera L.) tea, with the highest free-radical scavenging capacity among all teas tested. The antioxidant properties of L. speciosa tea, particularly when subjected to freeze-drying during the drying process, were significantly enhanced, possibly attributed to ellagitannins such as lagerstroemin, flosin, and reginin.

In PLOS One research published in 2025, antioxidant activities were robustly evaluated using DPPH, ABTS, superoxide, and nitric oxide assays, with the ethanol extract of L. speciosa demonstrating significant free radical scavenging (IC50 = 75.53 µg/mL for DPPH).

Evidence strength assessment: Antioxidant activity of the ellagitannin-rich fractions including lagerstroemin is well-supported at the in vitro level. No human clinical trials have been conducted specifically examining lagerstroemin's antioxidant effects.

5.4 Enzyme Inhibition: α-Amylase and α-Glucosidase

Using bioassay-guided separation, valoneaic acid dilactone was isolated from the banaba leaves as a potent α-amylase inhibitor. While this inhibitor is a structurally related compound rather than lagerstroemin itself, it shares the ellagitannin pharmacophore. Methanol and ethanol extracts of L. speciosa significantly inhibited α-amylase and α-glucosidase compared to standard acarbose, indicating substantial antidiabetic potential by delaying carbohydrate digestion and reducing postprandial glucose. The tannin-rich fraction, of which lagerstroemin is a component, is implicated in this enzyme inhibitory activity.

Among the ellagitannins, lagerstroemin possesses anti-diabetic properties, valoneaic acid dilactone displays potent inhibitory effect on xanthine oxidase, and ellagic acid inhibits the growth of HIV and human rhinoviruses.

Evidence strength assessment: Enzyme inhibitory data is primarily in vitro. The contribution of lagerstroemin specifically, as distinct from the total tannin/ellagitannin fraction or other co-constituents, has not been fully disambiguated in the available literature.

5.5 Additional Pharmacological Areas

The parent plant and its extracts have been investigated for a range of additional activities. Lagerstroemia speciosa possesses pharmacological effects that include antimicrobial, antioxidant, anticancer, antidiabetic, hypolipidemic, antiobesity, anti-inflammatory, analgesic, gastrointestinal, diuretic, thrombolytic, cardiovascular, central nervous system effects, inhibition of TNFα production, xanthine oxidase inhibition, hepatoprotective, and nephroprotective effects. However, it is important to note that most of these effects have been attributed to the whole plant extract and its many constituents collectively, not to lagerstroemin in isolation.

As of the available literature, there is no published scientific evidence confirming the anti-cancer efficacy of L. speciosa leaf extract in clinical settings.

6. Body Systems and Health Areas

Based on the available scientific literature, the body systems and health areas most associated with lagerstroemin and the banaba ellagitannin fraction include:

Endocrine / Metabolic System: Lagerstroemin is an ellagitannin that works as an insulin receptor activator by increasing tyrosine-phosphorylation of the β-subunit of the insulin receptor. This positions it as a potential insulin-sensitizing compound.
Cardiovascular / Lipid Metabolism: The beneficial effects of banaba and corosolic acid with respect to various aspects of glucose and lipid metabolism appear to involve multiple mechanisms, including enhanced cellular uptake of glucose, impaired hydrolysis of sucrose and starches, decreased gluconeogenesis, and the regulation of lipid metabolism.
Adipose Tissue: In vitro evidence demonstrates that lagerstroemin influences adipocyte glucose uptake and inhibits isoproterenol-induced lipolysis, suggesting a role in adipose tissue metabolism.
Oxidative Stress / General Cellular Health: The ellagitannin-rich banaba extract has demonstrated free radical scavenging and antioxidative activity relevant to protection from oxidative stress.
Urinary System: Folkloric use of banaba leaf decoctions for diuretic purposes has been recorded.

7. Dosage Forms and Reported Dosages

No dosage for isolated, purified lagerstroemin in human subjects has been established or reported in peer-reviewed clinical literature, as the compound has not been administered in isolation to human subjects in any identified clinical trial. The following dosages refer to banaba leaf extracts (which contain lagerstroemin as one of multiple active constituents), as reported in specific studies:

In a randomized clinical trial involving Type II diabetics, subjects received a daily oral dose of Glucosol (a banaba leaf extract standardized to 1% corosolic acid); daily dosages of 32 and 48 mg for 2 weeks showed significant reductions in blood glucose levels.
In a randomized, double-blind, placebo-controlled clinical trial, twelve patients with metabolic syndrome received banaba (500 mg) twice a day, before breakfast and dinner, for 12 weeks.
Twenty-four human subjects with mild type 2 diabetes were given three tablets of a Banabamin-based multi-ingredient product three times daily; a 13.5% average decrease in blood glucose levels was reported, and no adverse effects were observed.
An open label safety and efficacy study administered 100 mg tablets daily of a water soluble banaba extract to 15 subjects over 1 year; the extract was not standardized to a specific constituent.
In in vitro studies, lagerstroemin was able to induce phosphorylation of the β-subunit of the insulin receptor at 150 μM, and glucose transport stimulation was observed beginning at 40 μM, with an EC50 of 80 μM. These are cell-culture concentrations and cannot be directly translated to oral dosing recommendations.

Limited clinical trial data exist to provide dosing recommendations for banaba preparations or their constituent lagerstroemin.

8. Safety Considerations and Interactions

8.1 Acute and Sub-Acute Toxicity

A study aimed to investigate the acute and sub-acute oral toxicity of L. speciosa in Sprague-Dawley rats; acute toxicity was determined by a single oral dose of 2000 mg/kg, with animal behaviour and mortality rate observed for 14 days. The sub-acute study administered 200 mg/kg daily for 28 days, with body weight, organ weight, food and water intake, biochemical, haematological parameters, and histopathology studied. The findings showed no mortality or morbidity in acute and sub-acute toxicity studies in rats; additionally, no significant variations were found in the respective weight of organs, haematological and biochemical parameters of treated groups with reference to the control.

No toxicity has been reported in the available banaba literature. However, additional human efficacy and safety studies are warranted, particularly studies assessing dose- and time-dependent effects; investigations are needed to clearly define and understand the roles and importance of corosolic acid and related pentacyclic terpene acids relative to the ellagitannins present in banaba. Additional acute and subchronic animal safety studies are also needed.

8.2 Additive Hypoglycemic Risk

Because lagerstroemin functions as an insulin receptor activator and glucose transport stimulator, a pharmacodynamic interaction with conventional antidiabetic agents is plausible. The hypoglycemic effect of banaba has been attributed to both corosolic acid and ellagitannins (main active compounds of banaba) in animal models and several human studies. Concurrent use with insulin or oral hypoglycemic drugs could theoretically potentiate blood glucose-lowering effects, though this interaction has not been formally evaluated in controlled clinical studies.

8.3 Pregnancy and Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

8.4 Drug Interactions

Drug interactions with banaba are none well documented in the peer-reviewed literature. The potential for pharmacodynamic interactions with antidiabetic agents exists on theoretical mechanistic grounds, but has not been characterized in clinical pharmacology studies.

8.5 Overall Evidence Gaps

Evidence-based pharmacological research on Lagerstroemia and its constituents has largely been confined to in vitro screening and animal models, lacking clinical trials and bioactive compound isolations. This gap is especially notable for lagerstroemin as an isolated compound: all human data to date applies to whole-leaf extracts standardized to corosolic acid, and the attribution of any clinical effect specifically to lagerstroemin remains speculative pending dedicated human pharmacokinetic and pharmacodynamic studies.