Deng Xin Cao (Rush Pith, Juncus)

Chinese Herb Actions

Chinese Herb Dosage

• Why is the dosage of Deng Xin Cao so small?

  Because the herb is almost nothing but air. Our record gives 1.5–2.5 g and 1.5–4.5 g in decoction — roughly a fifth to a tenth of the 9–15 g typical of most decocted herbs. That is not a sign of potency or toxicity. Deng Xin Cao is the dried pith of a rush stem: a spongy, feather-light white cylinder with almost no density. A 2 g dose of rush pith is a visually large handful, comparable in bulk to a much heavier weight of root or bark. The dose looks tiny because the herb weighs almost nothing, not because it is strong.

  • Standard decoction — 1.5–2.5 g, or 1.5–4.5 g depending on the source. Some references go a little higher; up to about 9 g of the fresh material is sometimes cited.
  • Bulk, not weight, is the practical guide — dispensaries often handle it in bundles or by volume, and it is sometimes counted in lengths of pith rather than grams.
  • Charred form (Deng Xin Cao Tan) — used when the aim is to cool blood and stop bleeding rather than to move water.
  • Preparation quirk — because the pith is so light and fluffy it floats and is awkward to cut or powder; it is commonly moistened before processing, and it is often added to a decoction bundled or wrapped rather than loose.

  Source: our own herb record (both cited ranges); published materia medica consensus; physical description of the drug from the botanical and pharmacognostic literature. Reference only — not a prescription.

Chinese Herb Contraindications & Cautions

• Are there cautions for Deng Xin Cao?

  Deng Xin Cao is one of the gentler herbs in the materia medica, and its cautions follow from its cooling, water-draining nature rather than from any toxicity. Our record lists two:

  • Cold or deficiency in the Middle Jiao — do not use. A cold, draining herb further weakens an already cold, weak digestion.
  • Urinary incontinence — do not use. Promoting urination is exactly the wrong direction when urine is already leaking.

  Additional points: as a diuretic-type herb it is inappropriate where fluids are already depleted — marked yin deficiency, dehydration, or profuse sweating. Its paediatric use is long-standing and traditional, but children should be treated by a qualified practitioner rather than self-dosed, and persistent night crying or sleep disturbance in a child deserves a proper assessment. Burning or painful urination can indicate a urinary tract infection, which is a medical matter.

  Source: our own herb record cautions; published materia medica consensus. Reference note, not a safety guarantee — consult a qualified practitioner.

Chinese Herb Toxicity & Overdose

• Low. Deng Xin Cao is regarded as a mild, non-toxic herb with a long record of use including in children, and our own record classifies it as neither toxic nor endangered. No significant toxicity is reported at the small doses in which it is used. The only routine caution is the ordinary one for cooling, water-draining herbs: it is unsuitable for cold, deficient or fluid-depleted patients rather than intrinsically harmful.

  Source: our own herb record; published materia medica consensus. Reference note, not a safety guarantee.

Herb-Drug Interactions

• Does Deng Xin Cao interact with medications?

  No well-established clinical herb–drug interactions are documented. Two theoretical areas are worth practitioner awareness:

  • Diuretic medication — a general caution for any herb used to promote urination; combining with prescription diuretics is a matter for the prescriber, particularly where electrolytes or fluid balance are already being managed.
  • Renally cleared drugs (preclinical signal) — dihydrophenanthrenes isolated from Juncus effusus have been characterised as inhibitors of the organic anion transporters OAT1 and OAT3 (PMID 30892891). Those transporters handle the kidney’s secretion of a number of medicines. This is an in-vitro finding on isolated compounds, not on the crude herb at traditional doses, and no clinical interaction has been demonstrated — but it is a reasonable thing for a practitioner to be aware of in a patient on renally cleared drugs.

  (Precautionary reference notes, not demonstrated interactions.)

Western / Biomedical Research

Chinese Herb Clinical Studies & Research

Provided as research context — a summary of published biomedical study, not a therapeutic or medical claim.

• Is there modern research on Deng Xin Cao (Juncus effusus)?

  Yes — and unusually, the research lines up neatly with the traditional calming use. The characteristic constituents of rush pith are phenanthrenes, above all effusol and dehydroeffusol. In a bioactivity-guided study using two-microelectrode voltage clamp on recombinant GABA_A receptors, both compounds enhanced GABA-induced chloride currents in a concentration-dependent way and independently of the benzodiazepine binding site — the authors noted this may explain the herb’s traditional use as a sedative and anxiolytic in Chinese medicine (PMID 22271080, DOI 10.1055/s-0031-1298174). It is rare for a traditional indication and a laboratory mechanism to converge this directly.

  • Sedative and anxiolytic (animal) — dehydroeffusol produced dose-dependent anxiolytic effects in the elevated plus-maze and hole-board tests in mice and reduced locomotion in the open-field test, without impairing motor coordination on the rota-rod (PMID 21104609). Further phenanthrenes from J. effusus showed comparable anxiolytic and sedative activity (PMID 22017742).
  • Human trial (single, small, industry-funded, cognition endpoint) — a randomised, double-blind, placebo-controlled study in 41 older adults (average age 69) took a J. effusus extract powder enriched with dehydroeffusol once daily for 24 weeks and reported higher scores than placebo on clue-recall and clock-drawing tasks and on a dexterity assembly task, with no clinically observed adverse events (PMID 40068564, DOI 10.1016/j.nut.2025.112712). Note the limits carefully: very small sample, a single trial, a concentrated enriched extract rather than the decocted herb, cognition rather than any traditional indication, and funding and test material supplied by the manufacturers. Preliminary at best.
  • Charred form (animal) — both J. effusus and carbonised J. effusus reduced markers of D-galactosamine-induced acute liver injury in mice via the Nrf2 pathway, with the carbonised form performing best (PMID 38325836, DOI 10.1248/cpb.c23-00578). Interesting as a laboratory counterpart to the traditional raw-versus-charred distinction, though liver injury is not a traditional indication for the herb.
  • Anti-inflammatory (in vitro) — a water extract reduced inflammatory markers in oral keratinocytes (PMID 35028318).
  • Aroma of the dried rush (human, small) — a study of volatile organic compounds from dried common rush reported physiological and psychological relaxation effects in human participants (PMID 35162880, PMC 8834784, DOI 10.3390/ijerph19031856). Of interest given the material’s use in tatami mats; not a test of the medicinal preparation.

  Apart from the one small trial above, this is laboratory and animal work. It supports the plausibility of the traditional calming use; it does not establish clinical efficacy for anything.

  Note on our existing research entry: our record carried a citation to a 1983 Chinese-language clinical report of a rush-pith and tofu decoction in 30 cases of chronic nephritis. That source could not be independently verified from the available indexes, so it has not been carried forward here. The two chemistry papers previously listed (antialgal dihydrophenanthrenes, and antimicrobial DNA-binding photosensitizers) concern the plant’s ecology and photochemistry rather than its medicinal use, and have likewise been set aside in favour of the pharmacological literature above.

  Sources: PMID 22271080, DOI 10.1055/s-0031-1298174; PMID 21104609; PMID 22017742; PMID 40068564, DOI 10.1016/j.nut.2025.112712; PMID 38325836, DOI 10.1248/cpb.c23-00578; PMID 35028318; PMID 35162880, PMC 8834784, DOI 10.3390/ijerph19031856; PMID 30892891 (transporter inhibition). Research context, not a therapeutic claim.

Chinese Herb Notes

• How does Deng Xin Cao compare with Zhu Ye and Mu Tong?

  All three drain heat through the urine, but they differ in strength and in where their emphasis falls. Our own record sets out the comparison:

  • Deng Xin Cao vs Zhu Ye — Deng Xin Cao is better for painful urination with a burning quality; Zhu Ye is the more effective of the two for irritability and insomnia in adults.
  • Deng Xin Cao vs Mu Tong — Mu Tong clears Small Intestine heat through the urine more effectively. Mu Tong is bitter and cold; Deng Xin Cao is sweet, bland and only slightly cold, which makes it the gentler herb of the two.

  The pattern across all three: Deng Xin Cao is the mildest member of this group. That mildness is the reason it is favoured in children and in frail patients, and the reason it is more often a supporting herb in a formula than the lead.

  Raw or charred — does the processing change what it does?

  Yes, and this is one of the clearer examples of processing changing a herb’s direction. Unprocessed Deng Xin Cao regulates water flow and clears heat. Charred (Deng Xin Cao Tan), it cools the blood and stops bleeding instead. A prescription that specifies the charred form is not asking for the same action.

  Which formulas contain Deng Xin Cao?

  In our own collection Deng Xin Cao appears in two formulas, which between them cover both halves of its character: Ba Zheng San (Eight Herb Powder for Rectification), a strongly draining formula for damp-heat painful urinary dribbling, and Ding Xian Wan (Arrest Seizures Pill), where the Heart-clearing, spirit-settling side of the herb is what is wanted. (Traditional formula context, not treatment advice.)

  Source: our own herb record (comparison notes with Zhu Ye and Mu Tong; raw-versus-charred note) and our own formula links; published materia medica consensus. Traditional context only.