☯ TCM Properties
Opens the chest, clears the Lungs, resolves Phlegm, controls bleeding and removes toxins; Clears Heat, clears Damp-Heat, clears Deficiency Heat, invigorates the Blood, nourishes the Heart and promotes urination
Traditional Chinese Uses
Song Luo is the dried thallus of the beard lichens Usnea diffracta and U. longissima (Parmeliaceae), which hang from conifers in cool mountain forests; it is listed as a middle-grade medicine in the Shennong Bencao Jing. Bitter, sweet and neutral, it opens the chest, clears the Lungs and resolves Phlegm, clears Heat (including Damp-Heat and Deficiency Heat), stops bleeding, removes toxins, invigorates the Blood, calms the Heart and promotes urination. Traditionally it is taken for cough with copious phlegm, malarial fevers, indigestion with vomiting, irregular menstruation, conjunctivitis and edema, and applied externally to wounds, sores and infected ulcers, its antibacterial usnic acid underlying much of this use.
Western Herbalism Properties
Botanical Description
Song Luo is the dried thallus of fruticose lichens of the genus Usnea (Parmeliaceae), principally Usnea diffracta and U. longissima, that grow pendent from the branches of conifers in cool, humid mountain forests of southwestern China. The thallus is a pale greyish-green, hair-like, much-branched filament 10–80 cm long; each branch is round in section and contains a tough central white cord of densely interwoven hyphae surrounded by a soft photobiont layer of green algal cells. Cortical pores allow gaseous exchange. The lichen carries usnic acid and other characteristic dibenzofurans responsible for its bitter taste and antimicrobial activity. As a lichen it represents a symbiosis of fungus and alga, not a vascular plant.
Active Constituents
Usnic acid
Dibenzofuran derivative (lichen secondary metabolite)Concentration: Principal characteristic constituent of Usnea
The most abundant and characteristic metabolite of Usnea. It exhibits broad antibacterial (notably against Gram-positive bacteria and mycobacteria), anti-inflammatory, antiviral, antioxidant and wound-healing activity, but also uncouples mitochondrial oxidative phosphorylation, which underlies its dose-dependent hepatotoxicity.
Diffractaic acid
Depside (para-depside)Concentration: Major depside of U. diffracta
A characteristic depside of Usnea diffracta with reported antibacterial, anti-inflammatory, analgesic and antioxidant activity; contributes to the heat-clearing and toxin-resolving actions.
Barbatic acid and related depsides
DepsidesConcentration: Minor to moderate
Phenolic depsides that add to the antimicrobial and antioxidant profile of the lichen thallus.
Usenamines and related dibenzofurans
Dibenzofuran alkaloidal/amino derivativesConcentration: Minor constituents
A series of dibenzofuran compounds (including newly described usenamines) isolated from U. diffracta that show cytotoxic and antimicrobial activity in vitro.
Usnea polysaccharides
PolysaccharidesConcentration: Water-soluble macromolecular fraction
Lichen polysaccharides associated with antioxidant and immunomodulatory effects that may complement the toxin-resolving reputation of Song Luo.
⚠ Drug Interactions
Hepatotoxic drugs (acetaminophen, statins, methotrexate, isoniazid)
Usnic acid uncouples mitochondrial oxidative phosphorylation in hepatocytes, causing oxidative stress, hepatocyte necrosis and apoptosis. FDA received numerous reports of severe liver toxicity (including fatal cases and transplantation) from usnic-acid-containing supplements. Combining Usnea with other hepatotoxic agents plausibly compounds this risk.
Clinical note: Avoid concurrent use with hepatotoxic drugs and alcohol; monitor liver enzymes if used at all, and avoid in pre-existing liver disease.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| decoction | 6-15g | Daily | — | — | — |
Preparation Methods
Decoction
Parts: Whole lichen thallus (dried)
The dried lichen is decocted, traditionally 3-9 g, to clear heat and phlegm and resolve toxicity. Because of usnic acid hepatotoxicity, internal use should be brief and cautious.
Topical wash or powder
Parts: Whole lichen thallus
Applied externally as a decoction wash or fine powder to sores, wounds and skin infections, exploiting the antibacterial usnic acid content to resolve toxin and stop bleeding.
Clinical Studies
Phytochemical composition, antimicrobial activities, and cholinesterase inhibitory properties of the lichen Usnea diffracta Vain
Thirty compounds (dibenzofurans, depsides and aromatic phenolics) were isolated from Usnea diffracta and evaluated. Extracts and isolates showed antimicrobial and cholinesterase-inhibitory activity, providing a chemical basis for the heat-clearing and toxin-resolving traditional uses of Song Luo.
Severe hepatotoxicity associated with use of a dietary supplement containing usnic acid
Two previously healthy patients developed severe hepatotoxicity within three months of taking a usnic-acid-containing supplement; one required emergency liver transplantation for fulminant hepatic failure. Illustrates the serious dose-related liver toxicity of usnic acid, the principal constituent of Song Luo.
Historical Texts
Shennong Ben Cao Jing (The Divine Farmer's Classic of Materia Medica)
Han dynasty, compiled c. 200 BCE - 200 CEMing Yi Bie Lu (Miscellaneous Records of Famous Physicians), attrib. Tao Hongjing
Han-Wei, c. 3rd century CE (compiled)Ben Cao Gang Mu (Compendium of Materia Medica), Li Shizhen
Ming dynasty, 1596 CEReferences
- Hao YM, Yan YC, Zhang Q, Liu BQ, Wu CS, Wang LN. Phytochemical composition, antimicrobial activities, and cholinesterase inhibitory properties of the lichen Usnea diffracta Vain . Frontiers in Chemistry, Vol. 10, 1063645 (2023) [DOI]
- Sanchez W, Maple JT, Burgart LJ, Kamath PS. Severe hepatotoxicity associated with use of a dietary supplement containing usnic acid . Mayo Clinic Proceedings, 81(4):541-544 (2006) [DOI]
- Croce N, Pitaro M, Gallo V, Antonini G. Toxicity of Usnic Acid: A Narrative Review . Journal of Toxicology, 2022:8244340 (2022) [DOI]
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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