Lu Gen
StarPhragmites communis Trin.
☯ TCM Properties
Clears Heat and Drains Fire; Generates Fluids and Relieves Thirst; Eliminates Irritability; Stops Vomiting; Promotes Urination; Expels Phlegm and Discharges Pus; Vents Rashes
Traditional Chinese Uses
Lu Gen (reed rhizome) is a sweet, cold herb that gently cools and moistens without burdening digestion. It clears Heat from the Lungs and Stomach to address fever, thirst, dry mouth, and painful swallowing of early respiratory illness. Its mild action on the Stomach also settles nausea and vomiting caused by Stomach Heat. Because it simultaneously generates fluids and promotes urination, it helps restore fluid balance during febrile illness.
Western Herbalism Properties
Used In Formulas (1)
Botanical Description
Phragmites australis (Cav.) Trin. ex Steud. (Poaceae), commonly known as common reed and including the form formerly named Phragmites communis, is a tall, robust, rhizomatous perennial grass with a near-cosmopolitan distribution in temperate and tropical wetlands. It forms dense stands in marshes, ditches and along slow-moving water bodies. Plants spread by stout, hollow, creeping rhizomes and stolons, producing erect, hollow, smooth, unbranched culms 2 to 6 meters tall and up to 1.5 cm in diameter. The leaves are long, flat, lanceolate to linear blades 20 to 60 cm long and 2 to 4 cm wide, gray-green and arranged in two ranks, with a smooth, somewhat clasping sheath. The inflorescence is a large, plumose, somewhat one-sided terminal panicle 15 to 40 cm long, purplish to tawny at maturity, with many spikelets each bearing long silky hairs. The fresh or dried jointed white rhizomes, excavated in spring or autumn, constitute Lu Gen in Chinese medicine.
Active Constituents
Rhizoma Phragmitis polysaccharides (RPP)
Polysaccharide (branched arabinoxyloglucan)Concentration: Major water-soluble fraction; backbone of β(1→4)-linked glucopyranosyl residues branched at C-6 (xylose:glucose:arabinose:galactose ≈ 1:59:2:2)
Principal bioactive macromolecules of the rhizome. Demonstrate immunomodulatory, anti-inflammatory, antioxidant and hypoglycemic activity; certain fractions inhibit α-glucosidase and enhance glucose uptake and glycogen synthesis in insulin-resistant cells.
p-Coumaric acid
Hydroxycinnamic (phenolic) acidConcentration: Minor phenolic constituent
Antioxidant and antibacterial phenolic acid that contributes to free-radical scavenging and to the herb's reported heat-clearing, fluid-generating actions.
N-p-Coumaroyl serotonin
Phenolic amide (hydroxycinnamic acid amide)Concentration: Trace to minor (isolated from roots/rhizome)
Serotonin-derived phenolic amide with antioxidant and anti-inflammatory properties; isolated together with N-p-coumaroyl tryptamine from Phragmites roots.
N-p-Coumaroyl tryptamine
Phenolic amide (hydroxycinnamic acid amide)Concentration: Trace to minor
Tryptamine-derived phenolic amide co-isolated with N-p-coumaroyl serotonin; contributes antioxidant activity.
Phytosterols (β-sitosterol, campesterol, stigmasterol)
Steroid (phytosterol)Concentration: Minor
Plant sterols contributing anti-inflammatory and mild lipid-modulating effects.
Vitamins and free amino acids
Water-soluble vitamins (C, B1, B2) and amino acids (e.g., asparagine)Concentration: Variable, nutritionally relevant amounts
Contribute to the fluid-generating, thirst-relieving traditional use and provide antioxidant vitamin content.
Flavonoids and coumarins
Flavonoid / coumarinConcentration: Minor
Provide additional antioxidant and anti-inflammatory activity reported in phytochemical surveys of the rhizome.
⚠ Drug Interactions
Antidiabetic agents (insulin, sulfonylureas, metformin)
Phragmites polysaccharide fractions inhibit α-glucosidase and enhance cellular glucose uptake in vitro, which could theoretically add to the glucose-lowering effect of hypoglycemic drugs.
Clinical note: Only preclinical (in vitro) evidence; monitor blood glucose if large doses are combined with antidiabetic therapy.
Diuretics
The rhizome is traditionally used to promote urination; an additive diuretic effect is plausible but has not been quantified clinically.
Clinical note: Clinically minor at culinary/decoction doses; consider fluid and electrolyte status with high-dose loop or thiazide diuretics.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| decoction | 6-15g | Daily | — | — | — |
Preparation Methods
Decoction (dried rhizome)
Parts: rhizome
Typically 15–30 g dried rhizome decocted in water. Cut into short segments; because active volatiles and fluids are readily released, avoid excessively prolonged boiling. Used to clear heat, generate fluids, relieve thirst and irritability, and stop vomiting.
Fresh rhizome decoction / expressed juice
Parts: fresh rhizome
Fresh rhizome (30–60 g, up to 120 g) is preferred when strong fluid-generating and thirst-relieving action is desired; it may be decocted or crushed and the expressed juice taken. Fresh material is considered superior for clearing heat and generating fluids.
Clinical Studies
The physiochemical characteristics of Phragmites communis Trin polysaccharides and in vitro anti-diabetic effects of their different fractions
Characterized Phragmites polysaccharide fractions and showed potent α-glucosidase inhibition with enhanced glucose uptake and glycogen synthesis in insulin-resistant cells, supporting a hypoglycemic mechanism.
Genotoxicity evaluation of a Phragmitis rhizoma extract using a standard battery of in vitro and in vivo assays
A standard genotoxicity battery (Ames test, chromosomal aberration, micronucleus assay) found no genotoxic signal for Phragmitis rhizoma extract, supporting the safety of traditional use.
Historical Texts
Ming Yi Bie Lu (名医别录, Miscellaneous Records of Famous Physicians)
Southern & Northern Dynasties (c. 500 CE), attributed to Tao HongjingBen Cao Gang Mu (本草纲目, Compendium of Materia Medica)
Ming dynasty, 1596, Li ShizhenReferences
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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