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Cinnamomum cassia / verum (bark, oil)

Cinnamon

Cinnamon may lower blood sugar a little, but the evidence is mixed: a Cochrane review found it inconclusive, while later meta-analyses with much more variable trials found falls in fasting glucose and HbA1c.

The caution is coumarin: common cassia cinnamon carries enough that about 2 g a day reaches the European tolerable daily intake for a 60 kg adult, so heavy daily use should be Ceylon. The essential oil is a separate product that irritates and sensitises skin and burns the mouth if undiluted, and swallowing the dry powder by the spoonful (the "cinnamon challenge") can harm the lungs.

Updated
10 October 2026
Cinnamon sticks and ground cinnamon on a table
At a glance
Last reviewed 10 October 2026
Evidence
Limited
Best for
Blood sugar (type 2)
Typical form & use
Powder or capsule, 1.5–2 g daily
Onset
4+ weeks
Safety
Cassia coumarin can harm the liver at high intake. 3 known interactions, most serious with alcohol.
Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

UseEvidenceWhat the research shows
Blood sugar in type 2 diabetesCompare remedies for blood sugar →Limited

The 2012 Cochrane review (10 trials, 577 people, mostly cassia at about 2 g a day for 4 to 16 weeks, high or unclear risk of bias in most) found the effect on fasting glucose inconclusive and no difference in HbA1c, and concluded there was insufficient evidence.

A 2025 meta-analysis of 28 trials (3,054 people) found fasting glucose down by about 15 mg/dL and HbA1c down by about 0.56 points, but with very high heterogeneity (I2 88 to 100% for glucose and HbA1c) and results that depended on the trial. In a 6-week trial of 25 postmenopausal women, 1.5 g of cassia made no difference to glucose tolerance.

The best reading is a small, inconsistent effect at most, as an add-on and not a substitute for diabetes treatment.1,2

Blood sugar in prediabetesLimited

One double-blind trial in 54 adults with prediabetes (500 mg three times daily for 12 weeks) found fasting glucose stayed stable on cinnamon but rose by about 5 mg/dL on placebo, and glucose tolerance improved against baseline. It is a single small trial at two centres, so it does not show that cinnamon prevents diabetes.

A small crossover trial of Ceylon cinnamon (6 g) in 10 people with impaired glucose tolerance found no effect on glucose or insulin after a glucose drink, which is a reason not to assume all cinnamon behaves alike.3,4

Cholesterol and triglyceridesCompare remedies for heart health →Limited

A 2017 meta-analysis of 13 trials (750 people) found total cholesterol down by about 14 mg/dL and triglycerides by about 24 mg/dL, with no significant change in LDL or HDL.

A 2025 meta-analysis found LDL down by a few mg/dL in people with type 2 diabetes, mainly with capsules. The pooled trials differ widely in species, dose and length, and the authors of the Cochrane and 2017 reviews call for better trials. This is not a substitute for cholesterol treatment.2,5

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

Studied range (diabetes trials)
About 1.5–2 g a day for 4 to 16 weeks1,2,3
The Cochrane review's average dose was 2 g a day, mostly cassia. The 2025 meta-analysis found glucose falls at both 2 g or less and above 2 g, and HbA1c and insulin resistance falls only at 2 g or less. The prediabetes trial gave 1.5 g (500 mg three times daily). No source sets a recommended dose.
Coumarin tolerable daily intake (EFSA, BfR)
0.1 mg per kg body weight a day6,7
Cassia averages about 3,000 mg coumarin per kg, so BfR says a 60 kg adult reaches the limit at about 2 g of cassia a day and a 15 kg child at about 0.5 g. The same dose as a supplement can exceed the limit, so check the species on the label.
Cinnamon bark oil (irritant threshold)
Over 0.2 g a day is irritant (ESCOP, via EMA)8
The EMA assessment report quotes ESCOP saying cinnamon bark oil and cinnamaldehyde over 0.2 g a day are irritant, and that preparations with more than 0.01% cinnamaldehyde are suspect for skin reactions. Undiluted oil was strongly irritating to rabbit skin.
Timing · The diabetes trials used daily doses, often split across meals, for 4 to 16 weeks. No source identifies a best time of day.With food? · The sources we read give no food advice. As a spice in food it is a normal dietary use.How long to trial · Judge blood sugar by your own glucose or HbA1c measurements over 8 to 12 weeks, as the trials did, and tell whoever manages your diabetes that you are taking it. If nothing changes, the evidence suggests that is a common result.

How people take it

Ground bark (spice or capsule)1.5–2 g daily in trialsThe form used in most trials. Most trials used cassia, and capsule products vary in species and coumarin content. Ceylon (Cinnamomum verum, also sold as true cinnamon) contains only low levels of coumarin per BfR.
Water extractNot standardisedMentioned by the researchers who compared species as a way to cut coumarin exposure. We did not read a trial of a specific extract, so we cannot rate one.
Essential oilNot recommended to swallow or apply undilutedCinnamon bark oil is about 55 to 75% cinnamaldehyde. It irritates skin and eyes and is a skin sensitiser. We found no trial of the oil for any health use.

Safety

Who should avoid
  • High daily cassia intake — coumarin can damage the liver in sensitive people
  • Liver disease, or taking liver-toxic medicines, with cassia cinnamon
  • Undiluted cinnamon oil on skin or in the mouth — burns and allergic reactions are documented
  • Swallowing spoonfuls of dry cinnamon, including the "cinnamon challenge" — lung harm
  • Cinnamon or Peru balsam allergy — oral and skin reactions are documented
  • Children in large amounts — about 0.5 g of cassia reaches the limit for a 15 kg child
  • Replacing diabetes or cholesterol treatment — the evidence is mixed
Known interactions
MonitorAlcohol — The EMA report advises against swallowing cinnamon bark oil in liver conditions, alcoholism or with paracetamol, because cinnamaldehyde depletes glutathione in experiments.
MonitorDiabetes medication — Cinnamon lowered fasting glucose in some trials, so in theory it could add to glucose-lowering medicines; no source we read reports a case of harm, and the Cochrane review found adverse effects mild and infrequent.
MonitorStatins (cholesterol medication) — One case report describes acute hepatitis in a 73-year-old woman a week after starting cinnamon supplements while taking a statin, and the authors warn against combining cassia with liver-toxic drugs. A single case does not prove cause.

Questions people ask

Does cinnamon lower blood sugar?

Slightly at best. A Cochrane review found the evidence insufficient, and later meta-analyses found falls in fasting glucose and HbA1c but with very inconsistent trials. Use it, if at all, alongside your treatment, and check your readings.

What is the difference between cassia and Ceylon cinnamon?

Most supermarket cinnamon is cassia, which BfR says averages about 3,000 mg of coumarin per kg. Ceylon (Cinnamomum verum) contains only low levels.

Coumarin can harm the liver in sensitive people, so Ceylon is the better choice if you use cinnamon daily in larger amounts. Most diabetes trials used cassia, and the one Ceylon trial we read (10 people) found no glucose effect.

Is cinnamon oil safe to use?

Not undiluted. Cinnamon bark oil is irritant to skin and a skin sensitiser, caused burns after prolonged contact in a child, and irritates the mouth. We found no trial supporting any health use of the oil, and this page cannot say what dilution is safe for skin.

Is the cinnamon challenge dangerous?

Yes. Swallowing a spoonful of dry cinnamon is hard to do without inhaling it, and the fibres do not dissolve in the lungs. US poison centres reported 51 calls in 2011 and 178 in the first half of 2012, and inhaling it can cause coughing, choking and aspiration pneumonia.

Make it yourself

DIY guides that use cinnamon, with quantities, safety notes and an honest word on what they do.

A glass bottle of dark purple homemade elderberry syrup beside a small bowl of dried elderberries on a bright kitchen counter
How to Make Elderberry Syrup Safely at HomeEasy · 20 min hands-on
A glass jar and a bowl of golden homemade granola with nuts and seeds on a bright kitchen counter
How to Make Granola at Home (Lower-Sugar Recipe)Easy · 15 min hands-on

Sources (10)

  1. Cochrane review Leach MJ, Kumar S. Cinnamon for diabetes mellitus. Cochrane Database Syst Rev. 2012.
  2. Meta-analysis de Moura SL, Gomes BGR, Guilarducci MJ, et al. Effects of cinnamon supplementation on metabolic biomarkers in individuals with type 2 diabetes: a systematic review and meta-analysis. Nutr Rev. 2025.
  3. Randomised trial Romeo GR, Lee J, Mulla CM, Noh Y, Holden C, Lee BC. Influence of Cinnamon on Glycemic Control in Individuals With Prediabetes: A Randomized Controlled Trial. J Endocr Soc. 2020.
  4. Randomised trial Wickenberg J, Lindstedt S, Berntorp K, Nilsson J, Hlebowicz J. Ceylon cinnamon does not affect postprandial plasma glucose or insulin in subjects with impaired glucose tolerance. Br J Nutr. 2012.
  5. Meta-analysis Maierean SM, Serban MC, Sahebkar A, et al. The effects of cinnamon supplementation on blood lipid concentrations: A systematic review and meta-analysis. J Clin Lipidol. 2017.
  6. Regulator FAQ German Federal Institute for Risk Assessment (BfR). FAQ on coumarin in cinnamon and other foods.
  7. Toxicology review Abraham K, Wöhrlin F, Lindtner O, Heinemeyer G, Lampen A. Toxicology and risk assessment of coumarin: focus on human data. Mol Nutr Food Res. 2010.
  8. Regulator assessment report European Medicines Agency, HMPC. Assessment report on Cinnamomum verum J. S. Presl, cortex and corticis aetheroleum. EMA/HMPC/246773/2009. 2011.
  9. Perspective article Grant-Alfieri A, Schaechter J, Lipshultz SE. Ingesting and aspirating dry cinnamon by children and adolescents: the "cinnamon challenge". Pediatrics. 2013.
  10. Case report Brancheau D, Patel B, Zughaib M. Do cinnamon supplements cause acute hepatitis? Am J Case Rep. 2015.

Reader notes

Experiences and questions from readers, read by an editor before they appear. They are personal accounts, not evidence, and are not medical advice.

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Last reviewed 10 October 2026 · Next review April 2027 · How we rate evidence