GradedHealth

Cinnamon

Last reviewed October 2026 · Based on 21 studies

Bottom line

Several meta-analyses report lower fasting blood sugar with cinnamon, mainly in type 2 diabetes. HbA1c results are inconsistent, the trials are small and short, and the 2012 Cochrane review called the evidence insufficient. Cassia cinnamon contains coumarin, which can harm the liver in some people.

What it helps with

  • May lower fasting blood sugar — Mixed results, evidence grade C (Limited). Several meta-analyses of RCTs show lower fasting glucose, but the Cochrane review found it inconclusive and a 2023 dose-response review found no effect; direction is mixed. Downgraded for inconsistency and surrogate marker.
  • May lower HbA1c (blood sugar over the past few months) — Mixed results, evidence grade C (Limited). Two recent meta-analyses report significant HbA1c falls, but the 2012 Cochrane review, 2013 and 2019 meta-analyses and a 2023 dose-response review found none; HbA1c is a marker and the trials are small.
  • May lower blood sugar after meals — Mixed results, evidence grade C (Limited). Two meta-analyses report lower after-meal glucose, but a 10-person crossover trial of Ceylon cinnamon found no effect; evidence is limited and short-term.

What it is

Cinnamon is the dry bark and twig of Cinnamomum trees, used as a spice [1][2]. Its active compounds include cinnamaldehyde and procyanidins [2]. Cassia is the type most often used in trials [3]; Ceylon cinnamon is a different species with much less coumarin [2].

What the research says

Meta-analyses of randomized trials are the strongest evidence. Several report lower fasting blood sugar [4][5][6]. The 2012 Cochrane review found the fasting glucose effect inconclusive [3], and a 2023 dose-response review found no significant effect on fasting glucose or HbA1c [7]. HbA1c results conflict: a 2024 and a 2025 meta-analysis report significant falls [4][5], while a 2013 and a 2019 meta-analysis did not [8][6]. Two meta-analyses report lower blood sugar after meals [5][9], but a small crossover trial found no effect of Ceylon cinnamon after a glucose drink [10].

Doses used in studies

Doses in the trials ranged from about 120 mg to 6 grams a day, for 4 to 18 weeks [8]. One 2025 trial used 250 mg or 500 mg of Ceylon extract for four months [11]. Another used 4 grams a day of cinnamon spice for four weeks in prediabetes [12]. These are study doses, not recommendations.

Safety and interactions

Side effects are infrequent and generally mild in the trials [3], and digestive symptoms did not differ from placebo in one crossover trial [12]. Cassia contains coumarin, which can harm the liver in some people; heavy users may reach the EFSA tolerable daily intake of 0.1 mg per kg of body weight [13]. Liver enzymes did not change overall across seven trials [14]. Interactions with medicines are not well studied; one trial gave cinnamon with gliclazide, and its abstract does not report hypoglycemia [15]. No trial of cinnamon in pregnancy was found; a 2026 review mentions a pilot feasibility study of several spices in gestational diabetes, with no cinnamon-specific results, and says larger studies are needed [16]. No trial data on people with kidney disease were found.

Caveats and open questions

Results for fasting glucose and HbA1c vary widely between studies [8]. Most trials are small and short, and the Cochrane review found high or unclear risk of bias in most of them [3]. No trial in these reviews measured illness or death [3]. The 2025 Ceylon trial's authors hold a patent on the extract [11]. We found no head-to-head trial of Ceylon and cassia cinnamon.

References

  1. Cinnamon intake lowers fasting blood glucose: meta-analysis.. J Med Food, 2011.
  2. A critical appraisal of anti-hyperglycemic mechanisms, matrix-dependent bioavailability, and species-stratified safety of Cinnamomum spp. as functional food ingredients.. Food Res Int, 2026.
  3. Cinnamon for diabetes mellitus.. Cochrane Database Syst Rev, 2012.
  4. The effect of cinnamon supplementation on glycemic control in patients with type 2 diabetes mellitus: An updated systematic review and dose-response meta-analysis of randomized controlled trials.. Phytother Res, 2024.
  5. The effect of cinnamon supplementation on cardiovascular risk factors in adults: a GRADE assessed systematic review, dose-response and meta-analysis of randomized controlled trials.. J Health Popul Nutr, 2025.
  6. Efficacy and safety of cinnamon in type 2 diabetes mellitus and pre-diabetes patients: A meta-analysis and meta-regression.. Diabetes Res Clin Pract, 2019.
  7. The Effect of Cinnamon on Glycolipid Metabolism: A Dose-Response Meta-Analysis of Randomized Controlled Trials.. Nutrients, 2023.
  8. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis.. Ann Fam Med, 2013.
  9. Effects of cinnamon supplementation on metabolic biomarkers in individuals with type 2 diabetes: a systematic review and meta-analysis.. Nutr Rev, 2025.
  10. Ceylon cinnamon does not affect postprandial plasma glucose or insulin in subjects with impaired glucose tolerance.. Br J Nutr, 2012.
  11. Efficacy and Safety of Cinnamomum zeylanicum (Ceylon cinnamon) for diabetes mellitus: a randomized, double blind, placebo-controlled clinical trial.. Diabetes Metab Syndr, 2025.
  12. Effect of cinnamon spice on continuously monitored glycemic response in adults with prediabetes: a 4-week randomized controlled crossover trial.. Am J Clin Nutr, 2024.
  13. Toxicology and risk assessment of coumarin: focus on human data.. Mol Nutr Food Res, 2010.
  14. What is the influence of cinnamon supplementation on liver enzymes? A systematic review and meta-analysis of randomized controlled trials.. Phytother Res, 2021.
  15. Cinnamon extract improves fasting blood glucose and glycosylated hemoglobin level in Chinese patients with type 2 diabetes.. Nutr Res, 2012.
  16. [Role of spices in the management of diabetes and gestational diabetes].. Rev Med Suisse, 2026.