What it is
Cinnamon is the inner bark of trees in the Cinnamomum genus. Ceylon cinnamon (C. verum) comes mainly from Sri Lanka and has thin, papery layers and a mild, sweet taste. Cassia (C. cassia and relatives) comes from China, Indonesia and Vietnam; it is thicker, harder and stronger.
Cassia contains a lot of coumarin — on average about 3 g per kilogram, sometimes much more. Germany’s food-safety institute sets the tolerable daily intake at 0.1 mg per kg of body weight, so about 2 g of cassia a day is enough for a 60 kg adult to reach the limit. Ceylon contains only trace amounts.
What the research says
Blood sugar in type 2 diabetes
LimitedMany studies exist, but they rarely say which species was used, and results disagree. It is unclear whether cinnamon supplements help.
Amounts used in studies
Blood-sugar trials have used about 0.5–6 g a day. Two of our capsules provide 1 g of Ceylon cinnamon.
Who should avoid it
- Pregnancy, in supplement amounts.
- Liver disease, if the product is cassia.
- Never inhale or swallow dry cinnamon powder by the spoonful ("cinnamon challenge") — it can damage the lungs.
Medicines to watch
- Diabetes medicines: may add to blood-sugar lowering; monitor your levels.
- Medicines that affect the liver, if using cassia.
What to look for when buying
- Ask for species confirmation: the label should say Cinnamomum verum or C. zeylanicum.
- Ceylon costs several times more than cassia, so cheap "cinnamon" capsules are almost always cassia.
Common questions
How do I tell Ceylon from cassia in my kitchen?
Ceylon sticks are thin, brittle and rolled in many layers like a cigar. Cassia sticks are a single thick, hard curl.
Is a sprinkle of cassia on my oats a problem?
No. Occasional culinary use is fine. The concern is large daily amounts over a long time.
Read next
Sources
Last reviewed 19 October 2026 by Spicewell editorial team. How we write our guides
This guide is general information, not medical advice. Speak to a doctor or pharmacist before starting any supplement, especially if you are pregnant, breastfeeding, under 18 or taking medication.