Nao Yang Hua
StarRhododendron molle (Blume) G.Don
Traditionally used for
- Headaches
- Teeth & mouth
- Cough & breathing
- Pain & joints
- Heart & circulation
Cautions & contraindications
- Pregnancy
- Toxic — professional use only
☯ TCM Properties
Dispels Wind, expels Dampness, eliminates Blood Stasis and relieves pain
Traditional Chinese Uses
Nao Yang Hua is the dried flower of Rhododendron molle (Flos Rhododendri Mollis), classified among the wind-damp-dispelling substances. Pungent, bitter and warm, it enters the Lung and Liver channels to dispel Wind, expel Dampness, break up Blood Stasis and, above all, stop pain. It is a specialist remedy for stubborn wind-damp painful obstruction (bi) syndromes, rheumatic and rheumatoid joint pain, traumatic injury with swelling and bruising, intractable headache and toothache. It is usually applied externally as a wash, tincture or plaster, or taken internally only in minute doses within a formula.
Safety is paramount: the flower is highly toxic, its grayanane diterpenoids (rhodojaponins, grayanotoxins) causing potentially lethal cardiac and central-nervous-system poisoning. It is contraindicated in pregnancy, the weak and debilitated, and must never be self-administered.
Western Herbalism Properties
Relationships
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Botanical Description
Rhododendron molle (Blume) G.Don (Ericaceae), the Chinese yellow azalea, is a deciduous shrub 0.5-2 m tall, native to central and southern China and historically described from Japan. Young branchlets bear soft grey hairs. Leaves are alternate, oblong-elliptic to oblanceolate, 5-11 cm long, with bristle-fringed margins and pubescence on both surfaces. The conspicuous flowers appear in terminal clusters of 5-13 with or before the new leaves; the corolla is broadly funnel-shaped, 5-6 cm across, bright golden-yellow often with an orange or greenish blotch on the upper lobe, with five subequal lobes and ten exserted stamens. The fruit is an oblong capsule covered with stiff hairs. The dried flowers (Flos Rhododendri Mollis), called Nao Yang Hua or Yang Zhi Zhu, are highly toxic owing to grayanotoxins and were used in TCM to dispel wind, kill parasites, alleviate pain, and as a topical anaesthetic; the entire plant is poisonous to livestock, hence the name "sheep-stupefying flower."
Active Constituents
Rhodojaponin III
Grayanane diterpenoid (grayanotoxin-type)Concentration: Principal toxic and analgesic diterpenoid of the drug; present in flower, fruit, leaf and root, with content varying markedly by provenance, harvest time and processing
Binds neurotoxin site 2 of voltage-gated sodium channels and holds them in the activated, open state, causing prolonged membrane depolarisation in cardiac, neural and skeletal muscle tissue and a sustained rise in vagal tone. It is at once the main analgesic principle and the main lethal principle of the drug: antinociception in rodents appears at sub-milligram-per-kilogram doses and acute lethality follows within a small multiple of those doses, which is why an injectable rhodojaponin III product developed in China was abandoned.
Rhodojaponin VI
Grayanane diterpenoid (grayanotoxin-type)Concentration: One of the major diterpenoids quantified alongside rhodojaponin III in flower extracts
Shares the grayanane skeleton and the sodium-channel-activating action of rhodojaponin III. Rat pharmacokinetic work treats rhodojaponins II, III and VI as an integrated exposure whose combined plasma profile tracks the onset of arrhythmia after oral dosing of the flower extract.
Grayanotoxin I
Grayanane diterpenoidConcentration: Reported from the flowers; the isoform most often measured in grayanotoxin-contaminated honey
The archetypal grayanotoxin and the compound most often confirmed analytically in mad-honey poisoning. It produces the classic toxidrome of bradycardia, hypotension, atrioventricular block, nausea, salivation, dizziness and syncope by preventing sodium-channel inactivation.
Grayanotoxin III
Grayanane diterpenoidConcentration: Reported from the flowers, generally at lower abundance than grayanotoxin I
A high-affinity ligand of the voltage-gated sodium channel in excitable tissue, with the same cardiotoxic and neurotoxic profile as grayanotoxin I. Grayanotoxin I, rhodojaponin II and rhodojaponin III are the three isoforms singled out in the toxicology literature for the strongest channel binding.
Rhodomolleins
Grayanane diterpenoidsConcentration: A large family of structural variants (rhodomollein I, X, XII, XIII and many others) isolated chiefly from the flowers
Structurally diverse grayananes carrying most of the antinociceptive activity described in recent isolation work; several inhibit chemically induced nociception in mice at 0.4 to 20 mg/kg. Their toxicological behaviour has not been characterised compound by compound, so they cannot be assumed safer than rhodojaponin III.
Kalmanol
Kalmane-type diterpenoidConcentration: Minor diterpenoid reported from flowers and leaves
A rearranged grayanane relative found across toxic Ericaceae. It contributes to the diterpenoid burden of the drug rather than to any separate therapeutic action.
Quercetin
FlavonolConcentration: One of the flavonoids reported chiefly from flowers and fruits
A common dietary flavonol with antioxidant and anti-inflammatory activity in vitro. It is pharmacologically irrelevant beside the diterpenoids at the doses this drug is used in and should not be cited as a reason to consider the herb benign.
Kaempferol
FlavonolConcentration: Reported among the flavonoids of the flowers and fruits
Antioxidant flavonol of the flower fraction, without a demonstrated role in either the analgesic or the toxic action of the drug.
⚠ Drug Interactions
Digoxin
Grayanotoxins hold cardiac voltage-gated sodium channels open and raise vagal tone through the Bezold-Jarisch reflex; digoxin independently slows atrioventricular conduction and increases vagal tone. The two effects are additive on sinus rate and AV nodal conduction, and grayanotoxin poisoning alone already produces bradycardia, complete AV block and asystole in reported cases. There are no co-administration studies, but the shared endpoint is well characterised on both sides.
Clinical note: Do not combine. A patient on digoxin who takes this herb should be assessed with an ECG for bradyarrhythmia and AV block, and the herb stopped.
Beta-blockers (atenolol, metoprolol, propranolol, bisoprolol)
Grayanotoxin toxicity is dominated by bradycardia and hypotension driven by increased vagal tone. Beta-blockade removes the sympathetic reserve that would otherwise defend heart rate and blood pressure, so the same grayanotoxin dose produces deeper bradycardia and a greater fall in blood pressure. Case reports of grayanotoxin poisoning describe heart rates in the thirties and profound hypotension in patients with no cardiac drug on board at all.
Clinical note: Contraindicated together. Beta-blockade also blunts the compensatory tachycardia that would otherwise flag deterioration, so an apparently stable patient can be closer to collapse than the vital signs suggest.
Non-dihydropyridine calcium channel blockers (verapamil, diltiazem)
Verapamil and diltiazem depress sinoatrial and atrioventricular nodal conduction and lower systemic vascular resistance. Added to the grayanotoxin toxidrome of sinus bradycardia, AV block and hypotension, the combination attacks heart rate, conduction and afterload simultaneously with no compensating mechanism left.
Clinical note: Contraindicated together. Patients on rate-limiting calcium channel blockers should not be given this herb in any dose or preparation.
Class I antiarrhythmic drugs (quinidine, flecainide, lidocaine, propafenone)
Class I antiarrhythmics block the voltage-gated sodium channel; grayanotoxins bind the same channel at site 2 and prevent its inactivation. The pharmacology therefore collides directly at one molecular target, and the net effect on conduction cannot be predicted from either drug alone. Rat work shows that the plasma profile of the rhodojaponins tracks the appearance of arrhythmia after oral dosing of the flower extract, so an arrhythmic substrate is already present.
Clinical note: Avoid. Any patient taking an antiarrhythmic drug who has ingested this herb needs continuous cardiac monitoring rather than a dose adjustment.
Atropine
The bradycardia and hypotension of grayanotoxin poisoning are largely vagally mediated, so muscarinic blockade with atropine reverses them. Clinical series of grayanotoxin and mad-honey poisoning report that intravenous fluids plus atropine are almost always sufficient, with recovery typically within 24 hours.
Clinical note: This is the antidotal relationship, not a hazard: in suspected poisoning give intravenous crystalloid and atropine and obtain an ECG. Note the converse — a patient already on an anticholinergic drug may have a masked or atypical presentation.
Grayanotoxin-contaminated honey (mad honey)
Honey made by bees foraging on grayanotoxin-bearing Rhododendron nectar carries the same toxins as the herb. This is a genuine and separate exposure route: confirmed poisonings from imported honey are reported from Turkey, Nepal, Korea and a Hong Kong case traced to Rhododendron simsii, and the Rhododendron molle literature explicitly identifies mad honey as a grayanotoxin vehicle. A patient can therefore be carrying a grayanotoxin load that no medication history will reveal.
Clinical note: Ask specifically about imported or wild honey, honey given as a gift or a tonic, and traditional honey remedies, before and during any course containing this herb. In unexplained bradycardia with hypotension, take a honey history.
Ethanol and medicinal wine preparations
The grayanane diterpenoids are lipophilic and are extracted more completely by ethanol than by water, so a wine or spirit maceration delivers a higher diterpenoid dose than a decoction of the same weight of herb. Ethanol independently causes vasodilatation and hypotension, compounding the cardiovascular depression. Traditional use of this drug in medicinal liquor is a recognised route to poisoning.
Clinical note: Treat alcohol extracts as a different and more dangerous product than a decoction; do not carry a decoction dose across to a tincture, and warn patients against home-made herb wines containing it.
Central nervous system depressants (benzodiazepines, opioids, general anaesthetics)
Grayanotoxin poisoning includes altered mental status, weakness, respiratory depression and dyspnoea alongside the cardiovascular effects. Adding a sedative or opioid burden compounds respiratory and central depression and obscures the neurological signs that would otherwise signal poisoning. The traditional use of the flower as an anaesthetic component points the same way.
Clinical note: Avoid concurrent sedatives. Confusion or drowsiness in a patient taking this herb should be treated as possible grayanotoxin toxicity, not attributed to the sedative.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| wine steep or powder | 0.6–1.5 g | — | — | — | ChP 2025. 浸酒或入丸散 — steeped in wine or in pills/powder. Not to be taken in large amounts or over a long period. Contraindicated in the debilitated and in pregnancy. Grayanotoxin-bearing. Corrected from a generic 9-15g decoction filler value generated from tcm_category. |
| wash | Appropriate amount | — | — | — | ChP 2025. 外用适量，煎水洗。 |
Evidence Tier
Strong evidence · 4 studiesRecorded studies by study design, strongest design at the top. This is a study-design tier only, not a GRADE rating: it does not weigh risk of bias, consistency or precision.
Systematic review / meta-analysis
1
1 verified · 0 unverified
Randomized controlled trial
0
Other clinical trial
0
Observational / case report
0
In vitro / animal
3
2 verified · 1 unverified
Show 3 studies
- The integrated pharmacokinetics of major rhodojaponins correlates with the cardiotoxicity after oral administration of Rhododendri Mollis Flos extract in rats
- Evaluation of Rhodojaponin III from Rhododendron molle G. Don on oral antinociceptive activity, mechanism of action, and subacute toxicity in rodents
- Antinociceptive grayanane-derived diterpenoids from flowers of Rhododendron molle
Other / unclassified
0
Verified: design read from PubMed for a DOI that resolves to the cited paper Unverified: taken from the study's recorded description
Clinical Studies
The efficacy and toxicity of grayanoids as analgesics: A systematic review
A systematic review of the grayanoid diterpenoids, the compound class that defines Rhododendron molle, weighing analgesic efficacy against toxicity. It concludes that grayanoids are potent analgesics whose development has been blocked by acute toxicity and a therapeutic window too narrow to exploit, and it collects the toxic endpoints reported for the class.
The integrated pharmacokinetics of major rhodojaponins correlates with the cardiotoxicity after oral administration of Rhododendri Mollis Flos extract in rats
Rats were dosed orally with an extract of the flower (Rhododendri Mollis Flos) and the plasma concentrations of the major rhodojaponins were combined into a single integrated exposure curve, which was then set against electrocardiographic changes. The integrated rhodojaponin exposure tracked the onset and course of cardiotoxicity, tying the arrhythmia directly to these diterpenoids rather than to any other fraction of the extract.
Evaluation of Rhodojaponin III from Rhododendron molle G. Don on oral antinociceptive activity, mechanism of action, and subacute toxicity in rodents
Rodent study of orally administered rhodojaponin III covering analgesic effect, mechanism and subacute toxicity in the same programme. It confirms oral antinociceptive activity and characterises the toxicity that limits it, and is the most directly relevant safety dataset for the isolated principal toxin of this herb.
Antinociceptive grayanane-derived diterpenoids from flowers of Rhododendron molle
Seventeen diterpenoids, twelve of them new, were isolated from the flowers and tested for antinociception in mice against morphine as control. Compounds inhibited nociception by 41.9 to 91.6 percent at 20 mg/kg, and single compounds were active at 2 mg/kg and 0.4 mg/kg, which shows how small a dose of these diterpenoids is pharmacologically active and therefore how narrow the margin to toxicity is.
⚠ Safety & Contraindications
- Pregnancy
- Toxic — professional use only
Contraindications
It is not suitable for taking too much or for a long time. Its use is prohibited in the weak and pregnant women.
Source: Xi S, Gong Y. Essentials of Chinese Materia Medica and Medical Formulas. Academic Press/Elsevier, 2017, pp. 113–114.
Historical Texts
Shen Nong Ben Cao Jing (Divine Husbandman's Classic of Materia Medica)
Han dynasty, compiled circa 25-220 CEBen Cao Tu Jing (Illustrated Classic of Materia Medica)
Northern Song dynasty, 1061Ben Cao Gang Mu (Compendium of Materia Medica)
Ming dynasty, 1596Hua Tuo Shen Fang (Divine Prescriptions of Hua Tuo) and the Ma Fei San anaesthetic tradition
Late Eastern Han dynasty, 184-220 CE, transmitted through later compilationsChinese Pharmacopoeia (Zhonghua Renmin Gongheguo Yaodian), Rhododendri Mollis Flos monograph
Modern national standard, current 2025 editionReferences
- Guo Xiaohong; Wang Lijuan; Ran Qiang; Li Yanyan; Leng Jing; Tang Ping; Yang Min; Yu Chao. A review of Rhododendron molle: traditional uses, clinical applications, phytochemistry, pharmacology, toxicology, pharmacokinetics and quality control . Frontiers in Pharmacology (2026) [DOI]
- Cai Yong-Qing; Hu Jian-Hui; Qin Jie; Sun Tao; Li Xiao-Li. Rhododendron Molle (Ericaceae): phytochemistry, pharmacology, and toxicology . Chinese Journal of Natural Medicines (2018) [DOI]
- Gunduz Abdulkadir; Turedi Suleyman; Russell Robert M.; Ayaz Faik Ahmet. Clinical review of grayanotoxin/mad honey poisoning past and present . Clinical Toxicology (2008) [DOI]
- Baral Sushil; Baral Binaya Kumar; Sharma Pranit; Shrestha Surendra Lal. Dried rhododendron flower ingestion presenting with bradycardia and hypotension: a case report . Journal of Medical Case Reports (2022) [DOI]
- Timalsina Ashal; Gaire Arjun; Acharya Roshan; Subedi Anupa; Shrestha Rojee; Suwal Aayusha. Grayanotoxin poisoning following fresh rhododendron flower ingestion: a rare case report from rural Nepal . International Journal of Emergency Medicine (2025) [DOI]
- Chen Yabo; Li Kun; Gong Yanting; Wang Xunkang; Zhu Ruiqing; Guan Mengyao; Lai Liyong; Jiang Yiping. Grayanane diterpenoids from Rhododendron molle: Structural diversity, mechanisms of antinociceptive action, and structure-activity relationships . Fitoterapia (2026) [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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