Cinnamon Bark
Cinamonum zeylanicum/cassia-Cortex
AKA Twak, Rou Gui
Lauraceae
Sweet, Pungent, Astringent
Materia Medica
Cinnamomum verum (syn. C. zeylanicum) and Cinnamomum cassia. Part used: inner bark (Cortex). Family: Lauraceae.
Key Takeaways
- Cinnamon is the inner bark of several Cinnamomum species. Ceylon (true) cinnamon and cassia are the two that matter, and most cinnamon sold in the United States is cassia.
- The bark is a warming carminative, circulatory stimulant, astringent, and antimicrobial with over two thousand years of documented use in Chinese, Ayurvedic, and Western traditions.
- Evidence for blood sugar support is mixed. Some trials and meta-analyses show modest reductions in fasting glucose, while a Cochrane review found the evidence insufficient. I label the tiers below.
- Cassia carries substantial coumarin, which can stress the liver in sensitive people at sustained daily intake. Ceylon carries only a trace. For daily therapeutic use, choose Ceylon.
- Coumarin is not the drug Coumadin. The concern with cassia is hepatic, not anticoagulant.
Educational content only. This monograph is not medical advice and is not a substitute for care from a qualified practitioner. Do not stop or change any prescribed medication, including diabetes medication, based on anything you read here.
Botany and the Two Cinnamons
Cinnamon is not one plant. It is the dried inner bark of several evergreen trees in the genus Cinnamomum, laurel family, and the two species you will actually meet in commerce behave differently enough that a monograph has to treat them side by side.
Ceylon cinnamon, Cinnamomum verum, still appears in older texts and on supplement labels under its synonym C. zeylanicum. It is native to Sri Lanka, and the name "true cinnamon" belongs to it. The bark is harvested from young shoots, the outer cork is scraped away, and the thin inner bark is rolled into quills.
Cassia cinnamon, Cinnamomum cassia, is native to southern China and is the species behind nearly all ground cinnamon on American grocery shelves. Indonesian cassia (C. burmannii) and Saigon cinnamon (C. loureiroi) are close relatives that grade with it commercially, and both run high in coumarin like Chinese cassia does.
| Character | Ceylon (C. verum) | Cassia (C. cassia) |
|---|---|---|
| Quill structure | Many thin, papery layers rolled together, like a cigar in cross section | One thick bark layer curled into a hollow scroll |
| Color | Tan to light brown | Reddish to dark brown |
| Taste | Delicate, sweet, citrus notes | Hot, strong, slightly bitter |
| Texture | Brittle, crumbles easily | Hard, snaps |
| Coumarin | Trace | Substantial, varies by batch |
| Typical price | Higher | Lower |
Their medicinal actions overlap heavily, which is why they share this entry. Both are dominated by cinnamaldehyde, both are warming carminatives and antimicrobials, and traditional systems used whichever species grew nearby. The meaningful split is coumarin content, covered in its own section below.
Key Constituents
Cinnamaldehyde makes up roughly 60 to 80 percent of the bark's volatile oil in both species and drives the warming, carminative, and antimicrobial actions. It is also the compound responsible for cassia's skin sensitizing potential.
Coumarin occurs at meaningful levels in cassia and its relatives, and at only trace levels in Ceylon. It is the single most important compound for sourcing decisions.
Type-A polymeric procyanidins are water soluble tannin-related compounds studied for insulin signaling activity in laboratory work. They survive in the defatted, water extracted fraction, which matters for how you prepare the bark.
Eugenol is concentrated in Ceylon leaf oil rather than bark, one reason leaf and bark essential oils are not interchangeable.
Tannins give the bark its astringency and its traditional use against diarrhea and passive bleeding.
Energetics
Warming to hot, pungent and sweet, drying. Cinnamon moves blood to the periphery, warms the core, and dries damp, stagnant digestion. Every major tradition reads it the same way, which is rare and worth noticing. It suits cold constitutions, cold hands and feet, sluggish digestion with gas and bloating, and conditions made worse by cold. It aggravates hot, dry, irritated states.
Traditional Use
Chinese medicine. Cassia bark is Rou Gui, one of the principal herbs for warming the interior and restoring kidney yang, indicated for cold limbs, weak low back and knees, cold-type digestive weakness, and poor peripheral circulation. The twig, Gui Zhi, appears in formulas from the Shang Han Lun of the second century and works more at the surface, releasing the exterior and moving blood in the channels. Bark and twig are dosed and used differently, and this monograph covers the bark.
Ayurveda. The bark, twak, reduces kapha and vata while increasing pitta. It appears in digestive formulas alongside cardamom and bay in the classical trio known as the three aromatics, and in circulatory and respiratory blends where its warmth carries other herbs outward.
Western herbalism. The Eclectic physicians of the 1800s valued cinnamon beyond its carminative role as a uterine hemostatic. King's American Dispensatory records its use for passive uterine bleeding and postpartum hemorrhage, often as a strong tincture. Contemporary Western practice keeps the carminative, astringent, and circulatory-stimulant uses: cold digestion, gas, diarrhea, and as a warming addition that improves the taste and delivery of less pleasant formulas.
Actions
Carminative, aromatic digestive stimulant, circulatory stimulant, astringent, antimicrobial and antifungal, hemostatic in traditional use, hypoglycemic (evidence mixed, see below), mild antiplatelet activity attributed to cinnamaldehyde.
One apparent contradiction deserves a sentence. Cinnamon shows up historically both as a hemostatic for uterine bleeding and as an emmenagogue that encourages menstruation. The resolution is dose and context: astringent tannins dominate in some preparations and uses, while the warming, blood-moving volatile oil dominates in others. This is also why therapeutic doses are avoided in pregnancy while culinary amounts are not a concern.
What the Research Shows
Evidence: Mixed human trials
Blood sugar. This is the most studied question and the honest answer is that results conflict. A 2003 trial in Diabetes Care by Khan and colleagues reported that 1 to 6 grams of cassia daily lowered fasting glucose, triglycerides, and LDL in people with type 2 diabetes. A 2013 meta-analysis by Allen and colleagues in Annals of Family Medicine pooled ten randomized trials and found modest reductions in fasting glucose and lipids, without improvement in HbA1c. A 2012 Cochrane review by Leach and Kumar concluded the evidence was insufficient to support cinnamon for diabetes. The trials used different species, different doses, and different durations, which explains much of the disagreement. My read: cinnamon is a reasonable supportive food for metabolic health and an unproven treatment. Nobody should adjust diabetes medication around it.
Evidence: Preliminary, mostly laboratory
Antimicrobial. Cinnamaldehyde and cinnamon oils show broad activity against bacteria and Candida in laboratory studies. This supports traditional use in food preservation and topical or oral rinse applications, and it does not establish cinnamon as an internal antimicrobial treatment.
Evidence: Preliminary human data
Blood pressure and circulation. Small trials suggest minor reductions in systolic pressure with regular intake. The effect size is too small and the trials too short to build a protocol on.
Evidence: Traditional, consistent across systems
Digestion. The carminative use has continuous documentation across Chinese, Ayurvedic, Greek, and European practice, and the German Commission E approved cinnamon bark for loss of appetite and dyspeptic complaints. Traditional consensus this broad is its own form of evidence, and for low-risk digestive use I weight it accordingly.
Coumarin: The Real Safety Question
Cassia and its relatives carry coumarin at levels that vary widely between batches. Ceylon carries only a trace. German food chemistry work by Woehrlin and colleagues measured cassia samples at thousands of milligrams per kilogram while Ceylon samples sat near the detection limit.
Coumarin can injure the liver in a susceptible subset of people at sustained intake. Germany's federal risk institute set a tolerable daily intake of 0.1 milligrams per kilogram of body weight, a threshold a daily teaspoon of ground cassia can reach or exceed for an adult, and reach faster for a child. The effect reverses when intake stops, and most people never experience it, but you cannot know in advance whether you are in the susceptible group.
Now the correction this topic always needs. Coumarin is not Coumadin. Plain coumarin does not thin the blood. The anticoagulant drug warfarin is a synthetic derivative several chemical steps removed, and articles claiming cassia "acts like a blood thinner because of coumarin" are repeating an error. Cinnamon does have mild antiplatelet activity from cinnamaldehyde, which is a separate and much smaller consideration, noted under cautions.
The practical rule is simple. Occasional culinary use: either species. Daily use, therapeutic doses, or children: Ceylon.
Contraindications and Cautions
- Pregnancy. Culinary amounts are fine. Avoid therapeutic doses and the essential oil, given the traditional emmenagogue use.
- Liver conditions. Avoid regular cassia. Use Ceylon if using cinnamon at all, and discuss with your practitioner.
- Diabetes medication. Possible additive glucose lowering. Monitor and involve your prescriber before adding therapeutic doses.
- Anticoagulant and antiplatelet drugs. Theoretical additive effect from cinnamaldehyde at high sustained doses. Culinary use is not a concern.
- Essential oil. Cinnamon bark oil is a strong dermal irritant and sensitizer and is not for internal use or undiluted skin contact. I do not use it in leave-on products, and I recommend the whole bark, infusions, and extracts instead.
- Hot, dry constitutions. Energetically aggravating. Reduce or pair with moistening herbs if the bark feels overheating.
Dosing Perspectives
Per the method of this materia medica, doses are attributed to named sources and disagreements are left visible.
- German Commission E: 2 to 4 grams of bark daily for appetite loss and dyspeptic complaints.
- Michael Tierra, Planetary Herbology: 3 to 9 grams of the bark, reflecting Chinese-style decoction dosing.
- Chinese materia medica (Bensky): Rou Gui at 1.5 to 4.5 grams, often added near the end of a decoction or taken as powder to preserve the volatile oil.
- British Herbal Pharmacopoeia: 0.5 to 1 gram of dried bark, three times daily, by infusion or equivalent.
- Eclectic practice, King's American Dispensatory: strong tincture in frequent small doses for passive uterine bleeding, a historical clinical use I include for the record rather than as a home protocol.
The spread from 1.5 to 9 grams is not sloppiness. The low end treats cinnamon as an aromatic where the volatile oil does the work. The high end treats it as a decocted constitutional herb inside a formula. Match the dose to the preparation and the goal, and for anything daily at the higher end, use Ceylon.
Preparations
Infusion. 1 to 2 teaspoons of crushed quills or a half teaspoon of powder per cup, covered, steeped 10 to 15 minutes. Covering matters because the medicine is partly in the steam you would otherwise lose.
Decoction. For Chinese-style formulas, simmer gently and add cinnamon in the final minutes.
Powder. The simplest route to food doses. Stir into warm milk, honey, oatmeal, or coffee.
Tincture. 1:5 in 50 to 60 percent alcohol, dosed by the drop as a warming carminative addition to formulas.
Honey infusion. Crushed quills steeped in raw honey for several weeks make a warming winter preparation that children accept without negotiation.
Frequently Asked Questions
What is Ceylon cinnamon?
Ceylon cinnamon is the bark of Cinnamomum verum, the species native to Sri Lanka known as true cinnamon. It tastes sweeter and more delicate than common cassia and contains only trace coumarin, which makes it the right choice for daily use.
Where does cinnamon come from?
Ceylon cinnamon comes mainly from Sri Lanka, with smaller production in Madagascar and the Seychelles. Cassia comes from China, Indonesia, and Vietnam. Nearly all ground cinnamon sold in American grocery stores is cassia.
How can I tell Ceylon from cassia at home?
Look at the quills. Ceylon rolls many papery layers into a dense scroll that crumbles when pressed. Cassia is a single thick layer curled into a hard hollow tube. Ground cinnamon is harder to distinguish, so with powder you are trusting the label.
Can dogs have cinnamon?
Small culinary amounts of Ceylon cinnamon are generally considered safe for dogs. Skip cassia for regular use because dogs are small and reach the coumarin threshold quickly, keep cinnamon essential oil away from them entirely, and never let a dog inhale loose powder, which irritates their airways.
Does cinnamon lower blood pressure?
Small human trials suggest a minor reduction in systolic pressure with regular intake. The effect is modest and the research is preliminary, so treat cinnamon as a supportive food rather than a blood pressure intervention.
Where should I buy Ceylon cinnamon?
Buy whole quills from a spice supplier that names the species and country of origin, ideally with batch testing. Whole quills keep their volatile oil far longer than powder, and you can grind as needed.
Sources
- Khan A, et al. Cinnamon improves glucose and lipids of people with type 2 diabetes. Diabetes Care. 2003.
- Allen RW, et al. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Annals of Family Medicine. 2013.
- Leach MJ, Kumar S. Cinnamon for diabetes mellitus. Cochrane Database of Systematic Reviews. 2012.
- Woehrlin F, et al. Quantification of flavoring constituents in cinnamon: high variation of coumarin in cassia bark. Journal of Agricultural and Food Chemistry. 2010.
- Abraham K, et al. Toxicology and risk assessment of coumarin. Molecular Nutrition and Food Research. 2010.
- German Commission E monograph, Cinnamomum bark.
- Bensky D, Clavey S, Stöger E. Chinese Herbal Medicine: Materia Medica, 3rd edition.
- Tierra M. Planetary Herbology.
- Felter HW, Lloyd JU. Cinnamomum, King's American Dispensatory, 1898. Public domain, hosted at Henriette's Herbal.