Cassia Bark (Cinnamomum cassia): A Comprehensive Reference
1. Identity: Botanical Classification, Nomenclature, and Natural Source
1.1 Botanical Identity and Taxonomy
Cassia bark is derived from Cinnamomum cassia, called Chinese cassia, cassia cinnamon, or Chinese cinnamon — an evergreen tree originating in southern China and widely cultivated there and elsewhere in South and Southeast Asia. Its accepted scientific name is Cinnamomum aromaticum Nees (family Lauraceae), with Cinnamomum cassia widely used as a synonym in commerce and the scientific literature. The standardized English common name is "cassia"; its Pinyin names in Chinese are rou gui (bark) and gui zhi (twig).
The tree grows to 10–15 m (33–49 ft) tall, with grayish bark and hard, elongated leaves that are 10–15 cm (3.9–5.9 in) long and reddish when young. Chinese cassia is a close relative to Ceylon cinnamon (C. verum), Saigon cinnamon (C. loureiroi), Indonesian cinnamon (C. burmannii), and Malabar cinnamon (C. citriodorum).
1.2 Cassia vs. True Cinnamon and Related Species
Cassia (Cinnamomum cassia) is a tree of the family Lauraceae, and the spice made from its aromatic bark is closely related to true cinnamon (Cinnamomum verum). Cassia bark has a more pungent, less delicate flavour and is thicker than cinnamon bark, and it contains 1 to 2 percent oil of cassia, a volatile oil the principal component of which is cinnamic aldehyde. Southern Europeans generally prefer it to true cinnamon, and in North America ground cinnamon is commonly sold without distinction as to the species from which the bark is obtained.
China and Vietnam grow Cinnamomum cassia, also called Chinese Cassia or Chinese Cinnamon. Cinnamomum loureirii, also known as Saigon Cinnamon, is farmed in Vietnam, while Cinnamomum burmannii, referred to as Indonesian or Pedang Cassia, is produced in Indonesia. The ground spices and extracts derived from these species are most commonly called Cassia.
1.3 Commercial Forms and Preparations
Traditionally, the bark is stripped off the tree and dried in the shade. Some varieties are scraped, and while drying the bark curls into quills. The colour varies from light reddish brown for the thin, scraped bark to gray for the thick, unscraped bark. Ground cassia is reddish brown in colour. Common commercial forms include:
- Whole bark (quills or sticks): Dried strips used as a culinary or infusion ingredient.
- Ground powder: Producers collect the bark from plants and dry it before grinding into a fine powder.
- Standardized capsules and tablets: Encapsulated bark powder or extract, used in dietary supplement products.
- Water-soluble aqueous extract: Used in some clinical trials; prepared by extracting the water-soluble polyphenolic fraction.
- Essential oil (cassia bark oil): Cassia essential oil, or cassia bark oil, is derived by steam distillation of the cassia bark, leaves and twigs.
- Cassia buds: Cassia "buds," perhaps inappropriately named, are the dried immature fruits of C. cassia, and they yield about 20% of volatile oil having a cinnamaldehyde content of around 80%.
2. Traditional and Historical Use
2.1 Traditional Chinese Medicine (TCM)
Cassia bark is an important drug of Oriental medicine. Cassia bark has been used for over 2,000 years in Traditional Chinese Medicine (TCM), where it is known as Rou Gui. It is classified as a warming herb that tonifies yang, invigorates blood, and disperses cold, commonly used in formulas to treat cold limbs, abdominal pain, kidney yang deficiency, and menstrual irregularities. Cassia bark is one of the fifty fundamental herbs in traditional Chinese medicine. In traditional Chinese medicine cassia bark is used as a tonic for the stomach, to warm the channels, disperse cold, promote urination, and ease headache.
Cassia cinnamon bark is also used in traditional Japanese herbal medicines (Kampo medicines). Kampo medicines are of two types: one is a preparation composed of the powdered extract of the herbs specific to each medicine, and the other is made by decoction — the extraction of the water-soluble substances by boiling the herbs.
2.2 Ayurvedic and Indian Traditional Medicine
In Ayurveda, cassia is sometimes used similarly to true cinnamon, known for stimulating digestion (deepana), relieving gas (carminative), and balancing kapha and vata doshas. In the Indian system of medicine known as Ayurveda, the plant has been documented as thermogenic, purgative, expectorant and diuretic, and it has been used in the treatment of leprosy, erysipelas, ulcer symptoms, cough, flatulence, dyspepsia, menstrual problems and tuberculosis.
2.3 Historical Use in the Ancient World and Europe
It is highly probable that the bark, now called cassia lignea, was known to the ancient Greeks and Romans. The buds were also used as a spice, especially in India, and were used by the ancient Romans. Historically, cassia was considered more affordable and accessible than true cinnamon and became a major spice in ancient trade routes, eventually becoming a staple in European, Middle Eastern, and Asian cuisine and medicine. In medieval Europe, following spice trade routes, cassia became known as "Chinese cinnamon." Apothecaries prized it in digestive bitters, and European herbalists described it as a mild stimulant and preservative.
2.4 Traditional Preparations
Traditional preparations across cultures have included decoctions (the bark boiled in water), infusions (bark steeped in hot water as tea), powder incorporated into multi-herb formulas, and topical applications of the essential oil. For centuries, cassia powder has been a cornerstone of Ayurvedic medicine and Traditional Chinese Medicine. Ancient healers used it to treat digestive issues, improve circulation, and restore balance in the body's internal systems, and cassia was traditionally administered in teas and herbal decoctions.
3. Key Constituents and Active Compounds
3.1 Volatile Oil: Cinnamaldehyde and Related Aldehydes
GC-MS analysis on the essential oil of Cinnamomum cassia stem bark led to the identification of cinnamaldehyde, 2-hydroxycinnamaldehyde (2-CNA), coumarin, and cinnamyl acetate. The E-cinnamaldehyde (92%–98%), Z-cinnamaldehyde (0.8%–2.7%), β-caryophyllene (0.4%–3.6%), coumarin (0.1%–1.6%), and α-ylangene (0.1%–2.7%) are components identified within C. cassia. Analytical studies have shown that cassia barks contain high contents of cinnamaldehyde (13.01–56.93 mg/g). Cinnamaldehyde is the dominant bioactive compound of the essential oil fraction and the principal contributor to cassia's characteristic aroma, flavour, and many of its pharmacological properties.
3.2 Polyphenols: Procyanidins and Flavanols
The bioactive constituents of cassia bark include principally cinnamaldehyde (55–85% of bark oil), Type-A procyanidins, and phenolic acids. The outer bark, inner bark, and leaves are the medicinal parts of cinnamon plant that are rich in cinnamaldehyde, A-type procyanidin, and B-type procyanidin. Cinnamyl acetate, epicatechin, catechin, and p-coumaric acid are among the most abundant polyphenols identified by HPLC analysis. Callus and suspension cultures of Cinnamomum cassia produce large amounts of condensed tannins; the precursors (−)-epicatechin and procyanidins B2, B4, and C1 have been isolated from callus cultures.
Analytical profiling identifies nine key components in cassia bark: procyanidin B2, cinnamtannin B1, coumarin, 2-hydroxycinnamaldehyde, cinnamyl alcohol, cinnamic acid, cinnamaldehyde, 2'-methoxycinnamaldehyde, and eugenol.
3.3 Coumarin
Coumarin is a hepatotoxic natural compound found in different Cinnamomum species such as Cinnamomum cassia, Cinnamomum loureiroi, and Cinnamomum burmannii, all commonly referred to as cassia. Most of the cinnamon on the market comes from China (Cinnamomum cassia) and contains significant amounts of coumarin (2.23 mg/g dry weight). True cinnamon (Cinnamomum zeylanicum) from Sri Lanka would be a better alternative, since its content of coumarin is negligible (<0.01 mg/g dry weight). The coumarin content of cassia is notably variable: coumarin levels in cinnamon ranged from 1,740 to 7,670 mg/kg in cassia powder. In conclusion, coumarin levels in cassia cinnamon can vary widely even within a single tree.
3.4 Other Minor Constituents
Cinnamic acid and related phenolic acids contribute to antioxidant capacity and may influence metabolic pathways related to glucose and lipid handling. Cassia is particularly rich in polyphenolic polymers that can act as antioxidants and may help modulate insulin signaling in experimental models. Eugenol and other minor constituents are present in smaller amounts, contributing to aroma and bioactivity.
3.5 Overall Phytochemical Profile Summary
More than 160 health-benefiting components have been isolated from cassia bark, including coumarin. The major classes are: (1) phenylpropanoids, principally cinnamaldehyde, cinnamic acid, cinnamyl alcohol, and cinnamyl acetate; (2) polyphenolic oligomers (A-type and B-type procyanidins, cinnamtannin B1); (3) flavanols (epicatechin, catechin); and (4) the benzopyranone coumarin.
4. Mechanisms of Action
4.1 Glycemic and Insulin-Sensitizing Mechanisms
Cinnamomum regulates glucose uptake by adipose tissue and skeletal muscles chiefly through enhanced expression of PPARγ and transportation of GLUT4 to the cell membrane. Increased synthesis of glycogen is another mechanism by which Cinnamomum exerts its glucose-lowering effect. Although cinnamaldehyde was proved to be the major compound responsible for the observed activity, the polyphenolic procyanidin dimers and tetramers also play a vital role in directly or indirectly influencing different metabolic pathways involved in hyperglycemia and metabolic syndrome.
Research has hypothesized that the plasma membrane protein transient receptor potential ankyrin-1 (TRPA1) is a pivotal target in insulin resistance, and investigations of the mechanism of cinnamaldehyde (CIN) — an electrophilic TRPA1 agonist — in skeletal muscle, a primary insulin target, show effects on insulin resistance, hepatic glycogen accumulation, and muscle and adipose tissue glucose uptake. The effects of CIN on insulin resistance were mediated by TRPA1, with downstream signaling involving the activation of PI3-K, MAPK, PKC, as well as extracellular calcium and calcium release from intracellular stores.
In vitro experiments suggest that methylhydroxychalcone polymer (MHCP) functions by activation of cell receptors, presumably insulin receptors. More recently, it has been suggested that the polyphenols in cinnamon, specifically polyphenol A, are responsible for decreases in blood glucose witnessed in some studies.
4.2 Anti-Inflammatory Mechanisms
The anti-inflammatory effects of cinnamaldehyde are rooted in inhibiting the NF-κB pathway and reducing pro-inflammatory mediators like interleukins and TNF-α, which is beneficial for treating gastritis, ulcerative colitis, and rheumatoid arthritis. For example, in H. pylori-induced gastritis, cinnamaldehyde suppresses NF-κB activation and IL-8 expression in AGS cells.
4.3 Antimicrobial Mechanisms
In its antimicrobial action, cinnamaldehyde disrupts Salmonella and E. coli by affecting pilin levels and cell membrane integrity, curbing bacterial biofilms.
4.4 Antioxidant and Free Radical Scavenging
Cinnamaldehyde is well known for its anti-inflammatory, antioxidant, free radical scavenging, antimicrobial, antiparasitic, and antitumor properties. The polyphenolic procyanidins and cinnamaldehyde may act by their potent antioxidant activity and by regulating various proinflammatory cytokines and nitric oxide synthesis.
4.5 Lipid-Modulating Mechanisms
Cinnamaldehyde enhances metabolic health by improving glucose uptake and insulin sensitivity and offers cardiovascular protection through its anti-inflammatory and lipid-lowering effects. In animal studies, CIN also ameliorated the serum lipid profile and improved triglyceride tolerance following acute in vivo exposure.
4.6 Cytochrome P450 Interactions
Cinnamon extracts have been shown to inhibit multiple cytochrome P450 enzymes (CYP1A2, 2C9, 2D6, 3A4), potentially affecting the metabolism of blood thinners and other medications.
5. Scientific Evidence by Area of Use
5.1 Blood Glucose Regulation and Type 2 Diabetes
This is the most extensively studied area of cassia bark's clinical potential. Evidence is substantial but mixed, and the overall picture from pooled analyses is inconsistent.
Early landmark trial: The original influential clinical trial involved sixty untreated type II diabetics and explored fasting blood glucose levels in groups supplementing with varying doses of cinnamon at each meal for forty days. This trial, conducted by Khan et al. (2003), reported significant reductions in fasting blood glucose, total cholesterol, LDL cholesterol, and triglycerides. However, it used cassia bark specifically at doses of 1, 3, and 6 g/day.
Comparative review (2007): One systematic review identified seven clinical studies on various medical conditions including type 2 diabetes. Two of three randomized clinical trials on type 2 diabetes provided evidence that cassia cinnamon demonstrates a therapeutic effect in reducing fasting blood glucose by 10.3%–29%; the third clinical trial did not observe this effect.
Individual RCT (2007) — negative result: In one trial, sixty type 2 diabetic patients were randomized to either 1.5 g/day of cinnamon cassia powder or placebo, both in combination with their current treatment (metformin or sulfonylurea), in a single-blind, randomized, placebo-controlled trial over a 12-week period. After 12 weeks, HbA1c decreased similarly in both groups — from 8.14% to 7.76% in the cinnamon group and from 8.06% to 7.87% in the placebo group. This was not found to be statistically significantly different.
Small RCT (2012) — positive result: Eighteen type II diabetics participated in a 12-week trial; half received 1,000 mg of Cinnamomum cassia while the other half received 1,000 mg of a placebo pill. All subjects in the cinnamon group had a statistically significant decrease in their blood sugar levels (P = 3.915 × 10−10).
Comparative clinical review (2020): A review searching PubMed, Cochrane Library, and ScienceDirect from 2000 to April 2018 for clinical trials included a total of twenty-five studies (n = 997). Among these, fifteen studies investigated the effects on type 2 diabetes mellitus patients (n = 831), and nineteen used C. cassia. Results suggested C. cassia helped manage diabetes at 3–6 g per day, while the effectiveness of C. verum remained inconclusive.
RCT in impaired glucose tolerance (2014) — negative result: Twenty-one subjects with impaired glucose tolerance were included in a study matched for age, gender, and BMI, with capsules equivalent to 6 g cinnamon twice a day for 12 weeks, measuring insulin resistance by euglycaemic-hyperinsulinaemic clamp along with blood pressure, lipid profile, and liver enzymes. This study found no significant change in insulin sensitivity.
Updated meta-analysis (2021) — largely negative pooled result: An updated systematic review and meta-analysis searched multiple major databases including PubMed, Medline, Embase, CINAHL, and the Cochrane Central Register (last search December 30, 2020). Weighted mean differences were calculated using the random-effect model, and the pooled analysis found an insignificant reduction of the outcome variables (p > 0.05).
Umbrella review (2025): The findings of a 2025 umbrella review of meta-analyses of randomized controlled trials indicate that cinnamon supplementation is significantly associated with improvements in fasting blood glucose and lipid profiles, with more pronounced effects observed in patients with diabetes and metabolic syndrome. Subgroup analyses suggest that higher doses (>1.5 g/day) and shorter intervention durations (≤2 months) may enhance these benefits. Additionally, cinnamon shows potential in modulating insulin resistance, antioxidant capacity, and blood pressure regulation.
Evidence assessment: The overall human clinical evidence on cassia bark for glycemic control is mixed. While a number of individual RCTs and some pooled analyses report modest reductions in fasting blood glucose, other well-controlled trials find no significant effect, particularly for HbA1c. Methodological heterogeneity — including variability in dose (ranging from 120 mg to 6 g/day), duration, the form of cassia used, and patient populations — substantially limits interpretation. No regulatory health authority has approved cassia bark as a treatment for diabetes.
5.2 Lipid Profile Modulation
A meta-analysis showed that cinnamon significantly decreased blood triglycerides and total cholesterol levels but did not affect blood LDL-cholesterol and HDL-cholesterol levels. The updated 2021 meta-analysis also evaluated total cholesterol, triglycerides, LDL, and HDL as outcome variables. The evidence for lipid improvement is similarly mixed across trials; effects on LDL and HDL specifically remain inconsistent, and none of the findings have been replicated at scale with sufficient methodological rigor.
5.3 Blood Pressure
Cinnamon shows some potential in blood pressure regulation based on pooled analyses of RCTs. Research from 2024 shows that cinnamon effectively prevents and treats cardiovascular diseases by lowering blood pressure and lipids, and is also thought to improve the balance of oxidants and antioxidants. However, the authors of that review note that researchers must conduct more clinical studies. Current evidence is preliminary.
5.4 Antimicrobial Activity
Cinnamomum cassia has been traditionally used to treat dyspepsia, gastritis, blood circulation disturbances, and inflammatory diseases. Its major components cinnamaldehyde, cinnamic acid, and cinnamyl alcohol were reported to have various biological activities. Clinical study data includes one trial on Helicobacter pylori infection, one on oral candidiasis in HIV, and one on chronic salmonellosis. These represent very small bodies of evidence, each from single trials. Most antimicrobial data derives from in vitro or animal studies, not from adequately powered human clinical trials.
5.5 Antioxidant Activity
Studies have found cassia bark to have antioxidant, anti-microbial, and anti-inflammatory effects. Most antioxidant evidence is derived from in vitro assays or animal studies. Human trials specifically evaluating oxidative stress markers in the context of cassia bark supplementation are limited.
5.6 Anti-Cancer Properties
One in vitro study indicates that cinnamaldehyde was the most potent antiproliferative constituent of C. cassia, and its apoptotic mechanism in HepG2 cells could be mediated through the p53 induction and CD95 (APO-1) signaling pathways. Cinnamaldehyde exhibits notable efficacy against various cancers including breast, ovarian, and colorectal in preclinical models, by inducing apoptosis and hindering cell cycle progression, with molecular targets including NF-κB, AKT, and caspase pathways. The cassia bark exhibits promising anti-cancerous, anti-ulcerogenic, and anti-tumor properties in preclinical research. However, all cancer-related evidence is currently from cell culture and animal studies. No human clinical trial data exists to support anticancer claims for cassia bark.
6. Body Systems and Health Areas of Association
- Endocrine / Metabolic system: Blood glucose regulation, insulin sensitization, potential type 2 diabetes adjunct therapy.
- Cardiovascular system: Lipid modulation (triglycerides, total cholesterol); preliminary evidence for blood pressure effects; anticoagulant effects via coumarin content.
- Gastrointestinal system: Traditional use for dyspepsia, flatulence, abdominal pain, diarrhea, and gastritis; antimicrobial activity against H. pylori in vitro.
- Immune / Infectious: Broad-spectrum antimicrobial activity against bacteria and fungi (primarily in vitro and animal data).
- Musculoskeletal: Traditional TCM use for cold-type arthralgia and joint pain; anti-inflammatory mechanism via NF-κB inhibition.
- Reproductive system: Traditional TCM and Ayurvedic use for menstrual irregularities.
- Hepatic system (safety concern): Coumarin in cassia bark is a recognized source of potential liver toxicity at elevated doses (see Section 8).
7. Dosage Forms and Dosages Reported in Studies
Dosages used across clinical studies vary considerably. The following reflect doses as stated in specific cited sources:
- Cassia ground bark powder at 1–2 g/day for 90 days was the focus of one updated systematic review examining effects on plasma glucose and lipids in those with type 2 diabetes.
- A randomized, single-blind, placebo-controlled trial used 1.5 g/day of cinnamon cassia powder in a 12-week period.
- One 12-week trial used 1,000 mg of Cinnamomum cassia per day.
- A study used 5 g of encapsulated cassia cinnamon bark in a single acute dose to examine postprandial glucose response in obese women.
- One trial used capsules equivalent to 6 g cinnamon twice daily for 12 weeks in subjects with impaired glucose tolerance.
- In a UK-based trial on type 2 diabetics, cinnamon cassia bark powder capsules each contained 500 mg of cinnamon powder.
- A comparative clinical review suggested that C. cassia helped manage diabetes at 3–6 g per day.
- An umbrella review meta-analysis found that higher doses (>1.5 g/day) and shorter intervention durations (≤2 months) may produce more pronounced glycemic and lipid benefits.
Important note on dose forms: The pharmacological activity of cassia bark preparations varies substantially depending on whether whole powder, water-soluble extract, or ethanol extract is used, as these fractions contain different profiles of bioactive compounds. Trials have not been consistent in specifying extract type.
8. Safety Considerations and Drug Interactions
8.1 Coumarin Content and Hepatotoxicity Risk
Cassia cinnamon contains coumarin, a liver-toxic compound, which is absent or present in very low amounts in Ceylon cinnamon. When taken in high doses, coumarin poses a risk of liver toxicity, manifested by abnormal liver biology (increase in circulating concentrations of liver enzymes), which is reversible after cessation of exposure. At very high doses, it causes more serious liver damage (hepatic cytolysis, liver failure).
To limit dietary exposure, the European Food Safety Authority (EFSA) has set a Tolerable Daily Intake (TDI) of 0.1 mg/kg of body weight per day for coumarin. In 2004, the EFSA Scientific Panel concluded that coumarin was not genotoxic in experimental animals, allowing the derivation of a TDI. The overall No Observed Adverse Effect Level (NOAEL) for liver toxicity was found to be 10 mg/kg bw per day based on a two-year dog study.
Coumarin was at first suspected to have genotoxic and carcinogenic effects in humans, but new toxicological data have shown it to be non-genotoxic and made it possible to define a TDI. It is believed that most humans possess a major pathway for the metabolism of coumarin (the 7-hydroxycoumarin pathway) that differs from the more toxic 3,4-coumarin epoxidation pathway seen in rats.
Results in 47 cinnamon powder samples obtained from the German retail market confirmed high levels of coumarin in cassia cinnamon. A huge variation was observed in stick samples from two packages (range from below the limit of detection to about 10,000 mg/kg). This variability means that consumers cannot reliably estimate their coumarin intake from cassia-containing products.
In general, side effects are rarely caused by Kampo medicines containing cassia bark, but serious hepatotoxicity has been reported.
Adverse effects identified by vigilance schemes for food supplements mainly concerned the liver (hepatic cytolysis) and digestive symptoms (nausea, vomiting, abdominal pain).
8.2 Interaction with Anticoagulant Medications
Each teaspoon of cassia cinnamon contains approximately 5 mg of coumarin, while Ceylon cinnamon only contains trace amounts of the compound. Oral anticoagulants (like warfarin) are derived from coumarin, which inhibits the synthesis of vitamin K and prevents the formation of blood clots. Cinnamon may also interfere with the effectiveness of anticoagulant medications, thanks to the presence of coumarin. Coumarin can affect liver enzymes that help break down medications, particularly those in the cytochrome P450 family.
A published case report describes a fatal outcome: an 80-year-old man on dabigatran with a known history of non-valvular atrial fibrillation presented with haematemesis and black stool, which began 3 days after he had started taking a boiled mixture of ginger and cinnamon. Despite continuous aggressive resuscitation including administration of a reversal agent for dabigatran, bleeding could not be controlled and the patient died within 24 hours. The interaction of ginger and cinnamon with dabigatran led to fatal bleeding.
8.3 Interaction with Antidiabetic Medications
Cinnamon may interact with diabetes medications (like insulin or metformin) and blood thinners (such as warfarin). Both types of cassia can lower blood sugar excessively when combined with diabetes drugs, causing hypoglycemia. Cinnamon's compounds such as cinnamaldehyde may lower blood sugar levels and blood pressure, which can be problematic for individuals taking corresponding medications.
8.4 Cytochrome P450 Enzyme Inhibition
Cinnamon extracts have been shown to inhibit multiple cytochrome P450 enzymes (CYP1A2, 2C9, 2D6, 3A4), potentially affecting the metabolism of blood thinners and other medications. Coumarin found in cinnamon can affect liver enzymes and may lead to liver damage when combined with liver-metabolized medications like acetaminophen.
8.5 Allergic Reactions and Local Irritation
Some people have experienced mouth sores from eating products that contain cinnamon flavoring agents — a condition called cinnamon stomatitis. Cinnamon contains cinnamaldehyde, a compound that may trigger an allergic reaction when consumed in large amounts.
8.6 Regulatory Limits and Coumarin Labeling
A European study showed that a high share of commercial cinnamon samples — 66.3% — either did not fulfil quality criteria set by international standards, were not compliant with European food safety legislation, were suspicious of fraud, or could be toxic for children due to a high content of coumarin. These case reports and analytical findings suggest that deviation from the EFSA established ADI of 0.1 mg/kg bw has the potential to cause hepatotoxicity.
References
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