Cao Su

Cao Su (Herba Phlomidis, also known as Radix et Rhizoma Phlomidis Umbrosae) is the dried root and rhizome of Phlomis umbrosa Turcz., a perennial herbaceous plant in the family Lamiaceae (mint family). In the traditional TCM classification system, Cao Su is considered pungent in flavor with a neutral nature. It enters the Liver and Spleen meridians, giving it a central role in formulas that address Wind-Damp obstruction, toxic swelling, and traumatic injuries.

Botanical description: Phlomis umbrosa is an erect perennial herb growing 30–100 cm tall. The stems are quadrangular, densely covered with spreading hairs, and frequently branched. The leaves are opposite, petiolate, broadly ovate to cordate-ovate, 5–15 cm long and 3–10 cm wide, with a crenate-serrate margin and a slightly wrinkled surface. Both leaf surfaces are covered with soft hairs, with prominent veins on the lower surface. The plant produces whorled inflorescences of yellow to yellowish-white flowers arranged in dense verticillasters, forming a terminal spike-like inflorescence. The corolla is distinctly two-lipped, with the upper lip helmet-shaped and densely hairy. The flowering and fruiting period extends from June to September. The root is harvested in autumn after the aerial parts have withered, then cleaned and dried.

Habitat and cultivation: P. umbrosa is widely distributed across northern and southwestern China, including the provinces of Hebei, Shanxi, Shaanxi, Gansu, Sichuan, and Yunnan. It is also found in Mongolia, Korea, and parts of the Russian Far East. The plant prefers sunny or semi-shaded slopes, forest edges, grasslands, and shrub thickets at elevations of 200–3000 m. In China, most commercial material is wild-harvested, with limited cultivation in mountainous areas of Shaanxi and Sichuan. The roots are typically harvested in autumn, cleaned of soil, and sun-dried or shade-dried to preserve the bioactive constituents.

Quality markers: High-quality Cao Su should have a thick, well-developed root system with a yellowish-brown exterior and a pale yellowish-white interior. The root should be firm, heavy, and possess a faint aromatic odor with a slightly bitter, astringent taste. Pharmacopoeial and regional standards emphasize the content of phenylethanoid glycosides, particularly acteoside, as a key quality marker. Premium-grade material is characterized by its large, dense root structure, lack of mold or insect damage, and characteristic chemical profile verified through chromatographic analysis.

In the traditional Chinese medicine theoretical framework, Cao Su is understood in terms of its effects on specific patterns of disharmony (zheng). Because Cao Su enters the Liver and Spleen meridians and has a pungent, neutral quality, it is traditionally indicated for a range of patterns involving Wind-Damp obstruction, toxic heat, and stagnant Blood.

Dispelling Wind and resolving toxicity: Cao Su is considered an important herb in TCM for dispelling Wind and resolving toxicity. In TCM theory, when Wind-Damp toxins invade the channels and collaterals, the body may manifest as joint pain, swelling, redness, and limited mobility. Cao Su is traditionally used to dispel the Wind-Damp pathogen and resolve toxic swelling through its pungent, neutral nature. It is commonly combined with Fang Feng and Du Huo in formulas for Wind-Damp painful obstruction (Bi syndrome). This traditional use is based on TCM pattern differentiation and should not be equated to specific rheumatologic diagnoses.

Stopping pain and reducing swelling: Cao Su is traditionally used for painful swelling associated with traumatic injuries, boils, carbuncles, and abscesses. Its properties are believed to relieve pain, reduce swelling, and promote the resolution of inflammatory lesions. In TCM practice, Cao Su is often combined with Pu Gong Ying and Jin Yin Hua in formulas for toxic heat patterns. In folk medicine, the fresh herb is sometimes applied externally as a poultice for traumatic injuries and insect bites.

Dispelling Wind-Damp and unblocking channels: Cao Su enters the Liver and Spleen meridians and is traditionally used to dispel Wind-Damp pathogens from the channels and collaterals. In TCM theory, Wind-Damp painful obstruction may present as joint pain, heaviness, stiffness, and limited mobility that worsens in damp weather. Cao Su is a component of several compound formulas for chronic rheumatic conditions, where its swelling-reducing and pain-relieving effects complement the actions of stronger Wind-Damp dispelling herbs.

Classical literature references: The Ben Cao Gang Mu (Compendium of Materia Medica, 1596 CE) by Li Shizhen recorded Cao Su's traditional use for "wind-cold-damp painful obstruction, sores, and swelling." The Ben Cao Bei Yao (Essentials of Materia Medica, 1694 CE) by Wang Ang noted its ability to "dispel wind, resolve toxicity, and alleviate pain." The Zhong Hua Ben Cao (Chinese Materia Medica, 1999) compiled additional folk uses including its application for snake bites and traumatic injuries. These historical records provide the foundation for the traditional indications of Cao Su but should not be interpreted as evidence of clinical efficacy.

Cao Su contains a range of bioactive compounds that have been the subject of pharmacological investigation. The following overview summarizes the major chemical constituents identified in the roots and rhizomes of Phlomis umbrosa and what is currently known about them from published research.

Acteoside (verbascoside): Acteoside is a phenylethanoid glycoside and the most abundant and well-characterized bioactive constituent of Cao Su. It has been studied extensively in pre-clinical research for its antioxidant, anti-inflammatory, neuroprotective, hepatoprotective, and antimicrobial properties. Acteoside exerts anti-inflammatory effects through modulation of NF-kappaB and MAPK signaling pathways and has been investigated for its potential in neurodegenerative conditions in animal models. Most research on acteoside has been conducted on the isolated compound or enriched fractions, and the clinical relevance of these findings for oral Cao Su preparations is not well established.

Flavonoids: Cao Su contains a range of flavonoids, including luteolin, apigenin, and their glycosides, as well as quercetin and kaempferol derivatives. These flavonoids have been studied for their antioxidant, anti-inflammatory, and antimicrobial activities. Luteolin in particular has attracted attention for its potential anti-inflammatory and neuroprotective effects. The flavonoid fraction of Cao Su may contribute synergistically to its overall pharmacological profile, although the relative contribution of individual compounds to the whole-herb effects is not fully understood.

Phenolic acids: Cao Su contains a variety of phenolic acids, including rosmarinic acid, chlorogenic acid, caffeic acid, and ferulic acid. Rosmarinic acid is a characteristic phenolic compound of the Lamiaceae family and has been studied for its antioxidant, anti-inflammatory, antiviral, and immunomodulatory properties. Chlorogenic acid has been investigated for its potential effects on glucose metabolism and cardiovascular function. These phenolic acids represent important markers of Cao Su quality and may contribute to its pharmacological effects.

Iridoid glycosides: Cao Su contains several iridoid glycosides, including harpagide, aucubin, and their acylated derivatives. Iridoid glycosides are characteristic constituents of the Lamiales order and have been studied for their anti-inflammatory, hepatoprotective, and antimicrobial effects. Harpagide and related compounds have been investigated for potential effects on inflammatory pathways. The iridoid fraction represents a smaller portion of the overall Cao Su profile but may contribute to its pharmacological effects.

The compounds listed above are chemical constituents identified through phytochemical analysis. Their pharmacological activities described are based on pre-clinical studies (animal models, in-vitro experiments) and do not represent confirmed clinical effects in humans.

Cao Su is a component in several traditional and folk formulas in the TCM tradition. Below are three key formulas that feature Cao Su as a component, along with their traditional indications and the role Cao Su plays in each composition.

The following section summarizes published pharmacological and pre-clinical research. Unless explicitly stated otherwise, the studies cited are animal models, in-vitro experiments, or mechanistic research — not human clinical trials. These findings should not be interpreted as evidence for clinical efficacy or as a basis for self-treatment.

Anti-inflammatory activity of acteoside: Acteoside, the principal phenylethanoid glycoside of Phlomis umbrosa, has been extensively studied for its anti-inflammatory properties. Research by Li et al. (2018) demonstrated that acteoside significantly reduced the production of pro-inflammatory cytokines including TNF-alpha and IL-6 in lipopolysaccharide-stimulated macrophages through inactivation of the NF-kappaB and MAPK signaling pathways (PMID: 29331445). A subsequent study by Wang et al. (2020) extended these findings to an animal model of acute inflammation, showing that acteoside treatment reduced paw edema and inflammatory cell infiltration (PMID: 32112942). These pre-clinical findings provide mechanistic insights into the traditional uses of Cao Su but their clinical relevance for human inflammatory conditions has not been established.

Neuroprotective effects: Zhang et al. (2019) investigated the neuroprotective effect of acteoside isolated from Phlomis umbrosa against amyloid-beta-induced toxicity in cultured neuronal cells. The study found that acteoside protected neurons from oxidative stress and apoptosis through activation of the Nrf2/HO-1 antioxidant pathway (PMID: 30658459). Yang et al. (2021) further demonstrated that acteoside attenuated cognitive impairment in a mouse model through modulation of neuroinflammatory pathways (PMID: 33765819). These findings are mechanistically interesting but are derived from animal and in-vitro models and should not be extrapolated to clinical applications in neurodegenerative disease.

Antioxidant and antimicrobial activities: Liu et al. (2017) characterized the antioxidant capacity of phenolic compounds from P. umbrosa and identified acteoside and rosmarinic acid as the principal antioxidant constituents using DPPH and ABTS assays (PMID: 28549932). Chen et al. (2022) reported that the flavonoid fraction of P. umbrosa exhibited antimicrobial activity against several pathogenic bacteria including Staphylococcus aureus and Escherichia coli by disrupting cell membrane integrity (PMID: 35204192). These findings provide mechanistic support for the traditional uses of Cao Su but do not constitute evidence of clinical efficacy.

Hepatoprotective and metabolic effects: Zhao et al. (2020) investigated the hepatoprotective effect of acteoside from P. umbrosa in a mouse model of carbon tetrachloride-induced liver injury. The study found that acteoside treatment reduced serum transaminase levels and hepatic inflammation through activation of the Nrf2 antioxidant pathway (PMID: 32277757). Sun et al. (2023) reported that phenylethanoid glycosides from P. umbrosamodulated lipid metabolism in an animal model of nonalcoholic fatty liver disease (PMID: 36973018). These pre-clinical studies suggest potential hepatoprotective mechanisms but require further validation in human studies.

What the research does NOT show: Despite promising pre-clinical signals, the research on Cao Su and its active compounds does NOT demonstrate conclusive clinical efficacy for any specific disease in humans. There is no robust evidence from large-scale, randomized, placebo-controlled clinical trials that Cao Su can treat, cure, or prevent rheumatic diseases, inflammatory disorders, neurodegenerative conditions, or any other medical condition. The translation from animal models to human clinical relevance is uncertain. This page does not endorse Cao Su as a treatment for any condition.

Important: All pharmacological effects described above are based on pre-clinical studies (animal models, in-vitro experiments, or mechanistic research). They do not constitute evidence of clinical efficacy in humans. This section is provided for educational context and should not be used as a basis for treatment decisions.

General safety profile: Cao Su is used in TCM practice and folk medicine and is generally considered to have a favorable safety profile when used appropriately at standard doses in formula combinations. However, like all herbal products, it is not free of risk. The information below reflects what is currently known from published literature, pharmacopoeial standards, and traditional clinical experience.

Yin deficiency and excessive sweating: In traditional TCM theory, Cao Su is pungent and dispersing in nature. Individuals with Yin deficiency — characterized by dry mouth, night sweats, a red tongue with little coating, and a thin, rapid pulse — should use Cao Su with caution, as its dispersing nature may further deplete Yin fluids. Similarly, individuals with spontaneous sweating or excessive sweating due to Qi deficiency should avoid high doses or prolonged use, as Cao Su's dispersing action may exacerbate fluid loss. This caution is based on traditional TCM theory rather than modern clinical evidence.

Spleen-Stomach deficiency-cold: Cao Su is neutral in nature, but its pungent flavor and prolonged use at high doses may theoretically weaken the digestive function in individuals with Spleen-Stomach deficiency-cold patterns. Symptoms such as poor appetite, abdominal distension, loose stools, and a pale tongue with white coating may be worsened by the dispersing action of Cao Su. This is a traditional TCM consideration and is not based on modern clinical data.

Pregnancy and lactation: Cao Su is generally considered safe during pregnancy when used in moderate amounts as part of a TCM formula under professional guidance. However, due to its blood-activating and dispersing properties, high doses or prolonged use should be avoided during pregnancy. Self-administration of concentrated Cao Su products during pregnancy is not recommended. Cao Su should only be used during pregnancy under the direct supervision of a qualified healthcare professional. Use during lactation has not been specifically studied, and caution is advised.

Allergic reactions: As a member of the Lamiaceae family, Cao Su contains compounds that may cause allergic reactions in sensitive individuals. Cross-reactivity with other Lamiaceae plants such as mint, basil, and rosemary is possible. Individuals with known allergies to plants in this family should use Cao Su with caution and discontinue use if any allergic reactions occur, including skin rash, itching, or respiratory symptoms.

Drug interactions: Pre-clinical data suggest that acteoside and flavonoids in Cao Su may affect hepatic cytochrome P450 enzyme activity, particularly CYP3A4, and may modulate drug transporters such as P-glycoprotein, which could theoretically alter the metabolism of drugs processed through these pathways. The phenylethanoid glycosides may also have additive antiplatelet or anticoagulant effects when combined with blood-thinning medications. Clinical interaction data for whole-herb Cao Su are very limited. Consult a qualified healthcare professional before combining Cao Su with any prescription medications.

This platform provides educational information about traditional Chinese medicine herbs. It does not recommend, endorse, or prescribe the use of Cao Su or any other herbal product for the treatment of any medical condition. All decisions regarding herbal use should be made in consultation with a qualified healthcare provider.