“Ceylon or cassia” sounds like a connoisseur’s question, but for anyone considering cinnamon in gram-per-day amounts it is mostly a question about one compound: coumarin.
Quick answer: Cassia cinnamon (the common kind in grocery stores and most supplements) contains roughly 1% coumarin by weight, enough that a teaspoon or two a day can exceed established safety limits. Ceylon cinnamon contains only trace amounts. Most of the blood sugar trials used cassia, so Ceylon’s safety advantage comes with less direct evidence behind it. Neither species is a treatment for anything.
Why the species matters more than the brand
Several different trees are sold as “cinnamon.” The bark of Cinnamomum verum (also called zeylanicum), grown mainly in Sri Lanka, is Ceylon or “true” cinnamon. The bark of Cinnamomum cassia, C. burmannii (Indonesian), and C. loureiroi (Saigon or Vietnamese) are all cassia types. In the United States, the jar labeled simply “cinnamon” is almost always cassia, because it is cheaper, stronger-tasting, and more widely grown.
At the amounts you sprinkle on oatmeal, the distinction barely matters. It becomes important when people start taking cinnamon by the gram, every day, for months, which is exactly what the blood sugar studies did and what supplement labels encourage. If you have not yet read what the evidence actually shows for cinnamon and glucose, that is the context for everything below.
Coumarin: the actual difference
Coumarin is a naturally occurring aromatic compound found in many plants. It is what gives cassia part of its warm, sweet smell. The issue is that coumarin, in sufficient amounts, can injure the liver in susceptible people. European regulators set a tolerable daily intake of about 0.1 mg of coumarin per kilogram of body weight. For a 70 kg (154 lb) adult, that is roughly 7 mg a day.
Published food-safety analyses have measured cassia cinnamon powder at anywhere from about 2 to 12 mg of coumarin per gram, with variation by origin and batch. Ceylon cinnamon typically measures well under 0.1 mg per gram, often barely detectable. Put concretely:
- One level teaspoon of ground cinnamon is roughly 2.5 to 3 grams.
- A teaspoon of cassia could carry anywhere from about 5 to 30 mg of coumarin, which is at or well over the daily limit for an average adult.
- A teaspoon of Ceylon would carry a small fraction of a milligram.
Trials that used 3 to 6 grams of cassia per day therefore had participants consuming several times the tolerable intake for weeks. Most trials did not report liver enzyme data, so we do not have a good picture of how often that mattered. Case reports of liver enzyme elevations in people taking cinnamon supplements exist, and they are discussed in the side effects and liver article.
The coumarin in cinnamon is not the same as the anticoagulant drug warfarin, but they are chemically related, and the family name is why anyone on blood thinners should bring cinnamon up with their prescriber.
What the research used, and why that complicates things
Here is the awkward part. Most of the randomized trials that reported average reductions in fasting glucose used cassia, often C. cassia or C. burmannii, because it was what researchers could buy in quantity. A smaller number used C. verum or an aqueous (water-based) extract. There is no well-powered head-to-head trial comparing Ceylon and cassia for glucose outcomes in people.
That means a person choosing Ceylon for safety reasons is making a reasonable inference, that the active polyphenols are present in both species and that coumarin is not the active ingredient, but it is an inference, not a demonstrated finding. The polyphenol content of Ceylon and cassia does differ, and some lab studies suggest cassia extracts are more potent in cell assays. Whether that translates to any difference in people is unknown.
The study dose breakdown lists which species each major trial used, which is more useful than any general claim.
Water extracts: a third option
Coumarin is fat-soluble. Water-based cinnamon extracts, sometimes sold under proprietary names and standardized to a polyphenol percentage, remove most of it while retaining the water-soluble polyphenols that are thought to carry the glucose-related activity. A few trials used these extracts at a few hundred milligrams a day rather than grams of powder.
This is a legitimate approach to the coumarin problem, but it introduces its own label question: an extract’s potency depends on the extraction ratio and standardization, and bottles vary. A label that says “cinnamon extract 500 mg” without a species, extraction ratio, or standardization tells you very little.
How to tell them apart on the shelf and on the label
For whole sticks, the difference is visible. Ceylon quills are thin, papery, multi-layered, and crumble easily, like a rolled cigar. Cassia sticks are thick, hard, single-layer curls. For ground powder, you cannot tell by sight; Ceylon tends to be lighter in color and milder in taste, but that is not reliable.
On a supplement label:
- Cinnamomum verum or Cinnamomum zeylanicum means Ceylon.
- Cinnamomum cassia, aromaticum, burmannii, or loureiroi means cassia.
- “Cinnamon bark” with no species is almost certainly cassia.
- “Ceylon” printed on the front but a cassia species on the back has happened. Read the ingredients panel, not the front.
Some products state a coumarin content or say “low coumarin.” Independent testing has occasionally found products labeled Ceylon that were adulterated with cassia, so a third-party testing seal is worth more here than for most supplements. The supplement versus kitchen cinnamon article covers whether paying for a capsule makes sense at all.
Safety and interactions
The liver question above is the main species-specific concern. Beyond that, both species share the same cautions. Cinnamon oil and high doses of powder can irritate the mouth and gut, and allergic reactions to cinnamaldehyde occur in some people.
Hypoglycemia warning: Combining any blood-sugar-active supplement with insulin, sulfonylureas, or other glucose-lowering medicines can push glucose too low. Symptoms include shakiness, sweating, confusion, and a fast heartbeat. Do not add a supplement to a medication plan without your prescriber’s knowledge.
If you have fatty liver, which is common alongside metabolic syndrome, or you take medicines metabolized by the liver, high-dose cassia is a poor fit regardless of what the glucose studies say. The NCCIH page on cinnamon states the coumarin concern plainly: NCCIH: Cinnamon. For the broader picture of how cinnamon compares with other options, see the supplements for metabolic syndrome hub.
Questions to bring to your appointment
- Have my recent labs included liver enzymes (ALT, AST), and are they in a range where coumarin exposure is a concern?
- Do I have signs of fatty liver on imaging or labs that would change this decision?
- Am I on any anticoagulant or liver-metabolized medication that you would want to know about before I add cinnamon daily?
- If I use Ceylon rather than cassia, are you comfortable with the lower level of direct trial evidence behind that choice?
- Would a water extract be a reasonable middle ground, and what would you want to see on the label?
- If I try it, which lab value should we recheck and when?
About the author: Charles Kirkland is the founder of Metabolic Clarity Labs and author of The Journey Back. He is not a physician. This is general education, not a medically reviewed treatment plan.
Sources checked October 29, 2026. Discuss personal decisions with a qualified clinician or pharmacist. Do not start, stop, or change prescribed treatment based on this article.
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