Rou Gui
StarCinnamomum cassia Presl
Traditionally used for
- Colds & fever
- Digestion
- Urinary & fluids
- Fertility & vitality
- Pain & joints
- Heart & circulation
Cautions & contraindications
- Liver conditions
☯ TCM Properties
Tonifies Kidney Yang; Guides Fire Back to Its Source; Dispels Cold and Alleviates Pain; Warms the Channels and Disperses Cold; Tonifies Qi and Generates Blood
Traditional Chinese Uses
Rou Gui (cinnamon bark) is among the warmest and most potent herbs in Chinese medicine, used to restore and warm Kidney Yang, dispel cold from all channels, and invigorate Blood circulation. It is a primary herb for cold patterns involving the lower back and knees, frigid extremities, impotence, frequent urination, and abdominal pain from cold. Its capacity to return fire to its source — drawing floating Yang back to the Kidney — makes it essential in formulas for severe Yang deficiency with upward-floating heat signs.
Western Herbalism Properties
Used In Formulas (8)
Relationships
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Botanical Description
Cinnamomum cassia (L.) J.Presl (Lauraceae) is an evergreen tree native to southern China and mainland Southeast Asia, reaching 10 to 20 meters in height with a straight trunk and a dense, dark green crown; in cultivation it is often coppiced as a tall shrub or small tree for repeated bark harvest. The bark of mature trees is thick, rough and grayish-brown externally, with an inner bark of warm reddish-brown that is strongly aromatic. The leaves are alternate to subopposite, oblong to elliptic-lanceolate, 8 to 20 cm long, leathery, dark green and glossy above, paler beneath, with three prominent longitudinal veins running from the base. Small, fragrant, yellowish-white flowers are borne in axillary and terminal panicles, each with six perianth segments. The fruit is a small ovoid drupe seated in an enlarged cupule. The peeled, dried, naturally rolled inner bark constitutes Rou Gui, harvested in autumn from trees at least five to ten years old.
Active Constituents
(E)-Cinnamaldehyde
Phenylpropanoid (aromatic aldehyde)Concentration: Dominant component of the bark essential oil; the Chinese Pharmacopoeia requires not less than 85 percent (v/v) cinnamaldehyde in distilled cassia bark oil (Rou Gui You). Reported essential oil yield 0.41-2.61 percent w/w from stem bark and 2.70-3.11 percent w/w from branch bark.
The principal pungent and warming constituent of the bark and a TRPA1 agonist, responsible for the local vasodilator flush and much of the antimicrobial activity. It is also a moderate to strong skin sensitiser in the local lymph node assay, with EC3 values reported as low as 0.2 percent, which is a concern for topical cassia oil rather than for an oral decoction.
Coumarin
Benzopyranone (simple coumarin)Concentration: 2650-7017 mg/kg, mean 3856 mg/kg, across 60 retail ground cassia samples in one Czech market survey; approximately 12.07 mg per 4 g of cinnamon bark in Japanese Kampo decoction material. Cinnamomum verum bark is by comparison essentially coumarin-free (below the limit of detection in the same survey).
Cassia is the high-coumarin cinnamon, and coumarin is the reason Rou Gui carries a liver-safety caveat that Ceylon cinnamon does not. EFSA set a tolerable daily intake of 0.1 mg/kg body weight per day on the basis of hepatotoxicity in a two-year dog study; hepatotoxicity is thought to proceed through the minor CYP-mediated 3,4-epoxide pathway rather than the major 7-hydroxylation route. Coumarin is not itself an anticoagulant, a point routinely confused in consumer material: warfarin and dicoumarol are 4-hydroxycoumarins, a different chemistry.
Cinnamic acid
Phenylpropanoid (aromatic carboxylic acid)Concentration: Minor bark constituent, in part an oxidation product of cinnamaldehyde
A marker compound used alongside cinnamaldehyde in quality control of cassia bark. It is more water-soluble than cinnamaldehyde and so carries over into an aqueous decoction more reliably than the volatile fraction does.
Cinnamyl acetate
Phenylpropanoid esterConcentration: Secondary component of the bark volatile oil
Contributes to the aroma of the bark oil and is one of the volatiles whose proportion varies markedly with tree age and bark segment, which is part of why cassia bark quality is graded by thickness and oil content.
2-Methoxycinnamaldehyde
Phenylpropanoid (aromatic aldehyde)Concentration: Minor volatile constituent of the bark
A methoxylated analogue of cinnamaldehyde with reported anti-inflammatory and antiproliferative activity in cell models. The evidence is preclinical only and should not be presented as a clinical property of the decoction.
Procyanidin B2 and related proanthocyanidins
Condensed tannins (flavan-3-ol oligomers)Concentration: Non-volatile polyphenol fraction of the bark; (-)-epicatechin and procyanidins B2, B4 and C1 have been isolated
The water-soluble polyphenol fraction, and therefore the part of the bark most heavily represented in a decoction relative to the volatile oil. These oligomers carry most of the antioxidant activity and the in vitro insulin-signalling effects that motivated the cinnamon diabetes trials.
⚠ Drug Interactions
Warfarin and other vitamin K antagonists
The common claim that cassia thins the blood because it contains coumarin is pharmacologically wrong: plain coumarin has no vitamin K epoxide reductase activity, and the anticoagulant coumarins are 4-hydroxy derivatives. The plausible route is metabolic. Coumarin is a CYP2A6 substrate and cinnamaldehyde inhibits CYP2A6, while coumarin has been reported to affect CYP2D6 and CYP3A4. Documented case reports of INR disturbance attributable to cinnamon are sparse and confounded, so this remains a mechanistic rather than a clinically demonstrated interaction.
Clinical note: Culinary and ordinary decoction amounts are unlikely to matter. If a concentrated cassia bark extract is started or stopped in an anticoagulated patient, check the INR within one to two weeks rather than assuming either direction of effect.
Paracetamol (acetaminophen), methotrexate and other hepatotoxic drugs
Coumarin hepatotoxicity in susceptible individuals is the basis of the EFSA tolerable daily intake of 0.1 mg/kg body weight per day. The best human data specific to cinnamon bark as a medicine is a retrospective analysis of 129 Japanese outpatients on cinnamon-containing Kampo formulae: median coumarin intake was 0.113 mg/kg/day and 76 percent of patients exceeded the tolerable daily intake, yet abnormal liver function was no more frequent in that group (17.3 percent) than below it (19.4 percent), and no case was attributed to cinnamon bark. The honest reading is that the regulatory limit is regularly exceeded by therapeutic Rou Gui doses without a demonstrated signal, but that the margin over the limit is real and additive burden should not be ignored.
Clinical note: Do not treat the tolerable daily intake as a hard ceiling for short courses, but avoid open-ended daily high-dose cassia in patients with existing liver disease or on other hepatotoxic drugs, and check liver function if a course runs for months.
Metformin, sulfonylureas and insulin
Cassia proanthocyanidins improve insulin signalling in cell and animal models, and this drove a series of human trials. The Cochrane review of 10 randomised trials in 577 participants found insufficient evidence that cinnamon lowers HbA1c, fasting glucose or lipids, and the pooled trials mixed Cinnamomum cassia with other Cinnamomum species. An additive hypoglycaemic effect is therefore plausible but unproven.
Clinical note: No routine dose change is warranted. If a diabetic patient starts a high-dose cassia extract, ask them to monitor capillary glucose for the first fortnight rather than adjusting therapy pre-emptively.
Cinnamomum burmannii or Cinnamomum loureiroi supplied as Rou Gui
The commercial cinnamon trade does not respect binomials. Bark from Cinnamomum burmannii (Indonesian or Padang cassia) and Cinnamomum loureiroi (Saigon cassia) is sold interchangeably as cassia, and Cinnamomum burmannii in particular carries coumarin at the high end of the cassia range. Conversely, Cinnamomum verum sold as cinnamon is essentially coumarin-free but is not the drug Rou Gui names. Species identity therefore determines the single safety-relevant variable in this herb.
Clinical note: Source Rou Gui from a supplier that identifies the species and, for long courses, can supply a coumarin figure. A generic cinnamon certificate of analysis is not adequate for a drug whose only material hazard is species-dependent.
Gui Zhi (Ramulus Cinnamomi, cinnamon twig from the same plant)
Rou Gui is the thick trunk or branch bark and Gui Zhi is the young twig of the same species. They are separate Chinese Pharmacopoeia entries with different essential oil content and different classical indications, Rou Gui warming the interior and guiding fire back to its source, Gui Zhi releasing the exterior. Twig material has substantially lower volatile oil than trunk bark, so substitution under-doses the pungent fraction while leaving the label intact.
Clinical note: Confirm on receipt that the material is bark, not twig, and do not import Gui Zhi trial evidence into a Rou Gui monograph.
Dosage
| Form | Amount | Frequency | Duration | Population | Notes |
|---|---|---|---|---|---|
| decoction | 1–5 g | Daily | — | — | 中国药典 2020 【用法与用量】1～5g。 【注意】有出血倾向者及孕妇慎用；不宜与赤石脂同用。 【性味与归经】辛、甘，大热。归肾、脾、心、肝经。 — Chinese Pharmacopoeia 2020, quoted verbatim; route and cautions preserved. Replaces a cleared category-filler value. |
Dui Yao — Herb Pairs
The classical two-herb combinations this herb appears in, each with an action neither herb has alone.
Together they clear Heart fire and warm the Kidney, restoring communication between Heart and Kidney to calm the spirit.
Classic indication: insomnia and palpitations from Heart and Kidney failing to communicate.
Core pair of a classical formula — Jiao Tai Wan, Han Shi Yi Tong (Han Mao, 1522)
Two hot herbs that together warm and tonify Kidney yang and guide fire back to its source, more strongly warming the life-gate fire than either alone.
Kidney yang deficiency with cold limbs, sore lower back and impotence. Both are contraindicated in pregnancy and yin deficiency with heat.
Core pair of a classical formula — You Gui Wan, Jing Yue Quan Shu (Zhang Jingyue)
Evidence Tier
Strong evidence · 3 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
2
0 verified · 2 unverified
Randomized controlled trial
0
Other clinical trial
0
Observational / case report
1
0 verified · 1 unverified
In vitro / animal
0
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
Cinnamon for diabetes mellitus
Ten randomised controlled trials in 577 participants with type 1 or type 2 diabetes. The review found insufficient evidence to support the use of cinnamon for diabetes, with no significant difference from placebo, active medication or no treatment in HbA1c and inconsistent effects on fasting plasma glucose and lipids. Trial quality was poor and the pooled studies used more than one Cinnamomum species, so the result cannot be read as specific to Cinnamomum cassia.
The Relation between Hepatotoxicity and the Total Coumarin Intake from Traditional Japanese Medicines Containing Cinnamon Bark
Retrospective analysis of 129 Japanese outpatients prescribed a cinnamon-containing Kampo formula, with liver function measured before and after treatment. Coumarin content varied from 0.05 to 1.65 mg per gram of cinnamon bark and daily coumarin intake from 0.15 to 5.63 mg. Median intake was 0.113 mg/kg/day and 76 percent of patients exceeded the European tolerable daily intake of 0.1 mg/kg/day, yet the incidence of abnormal liver function was similar above and below that threshold (17.3 versus 19.4 percent) and no case of liver injury was attributed to cinnamon bark. This is the most directly relevant human safety dataset for medicinal cassia bark.
Efficacy of herbal medicine (cinnamon/fennel/ginger) for primary dysmenorrhea: a systematic review and meta-analysis of randomized controlled trials
Pooled randomised trials of cinnamon, fennel and ginger against placebo and against conventional analgesia in primary dysmenorrhoea. The herbs reduced pain intensity relative to placebo; the trials were small, heterogeneous and largely from a single region, and the cinnamon arms did not consistently specify the Cinnamomum species used, which limits how far the result can be attributed to Cinnamomum cassia bark specifically.
⚠ Rule-Based Cautions
These entries come from the deterministic rule tables that gate Verscienta's formula tools — classical pair prohibitions, pregnancy and lactation contraindications, and dose ceilings.
Incompatibilities (十八反 / 十九畏)
- 十九畏: Rou Gui × Chi Shi Zhi — avoid combining with Chi Shi Zhi / Halloysite
Historical Texts
Shen Nong Ben Cao Jing (Divine Husbandman's Classic of Materia Medica)
Eastern Han dynasty, compiled c. 200 CEBen Cao Gang Mu (Compendium of Materia Medica), Li Shizhen
Ming dynasty, 1596References
- Blahová J, Svobodová Z. Assessment of Coumarin Levels in Ground Cinnamon Available in the Czech Retail Market . The Scientific World Journal (2012) [DOI]
- EFSA Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (AFC). Coumarin in flavourings and other food ingredients with flavouring properties - Scientific Opinion of the Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food (AFC) . EFSA Journal (2008) [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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