Research dossier
Clinical research on Ceylon Cinnamon
8 trials reviewed across 3 indications.
Strongest evidence
Blood sugar & glycemic control
Mechanism
Cinnamaldehyde and related polyphenols appear to enhance insulin signaling, increase GLUT4 expression and glucose uptake, and slow gastric emptying — demonstrated mostly in cell and animal models, with weaker confirmation in humans.
The honest picture is mixed. Meta-analyses (Allen 2013, Davis 2011) show a modest fasting-glucose drop in type 2 diabetes, but even Allen found no HbA1c effect, the Cochrane review found insufficient evidence overall, and clean trials like Vanschoonbeek 2006 are flatly null. The foundational positive trial (Khan 2003) now carries an Expression of Concern. A small, real, but inconsistent and clinically uncertain effect — concentrated in diabetics, not healthy people.
Any benefit is confined to people with type 2 diabetes or metabolic syndrome. There is little evidence cinnamon improves glucose in metabolically healthy adults, and it is not a substitute for diabetes medication.
Trials cited
Cinnamon in type 2 diabetes (updated meta-analysis)
mixed · Meta-analysis
Allen et al., 2013, Annals of Family Medicinen=543The most-cited cinnamon meta-analysis (10 RCTs, 543 people with T2D). Cinnamon lowered fasting plasma glucose (~−24.6 mg/dL) and improved lipids — but, crucially, did NOT significantly change HbA1c, the gold-standard marker of long-term glucose control. A statistically real fasting-glucose signal that may not translate to meaningful diabetes management.
High between-trial heterogeneity and varied cinnamon species/doses. The absence of an HbA1c effect undercuts the practical importance of the fasting-glucose drop.
Cinnamon and fasting blood glucose (meta-analysis)
positive · Meta-analysis
Davis & Yokoyama, 2011, Journal of Medicinal Foodn=375Pooling 8 trials, cinnamon (especially concentrated extract) produced a modest but statistically significant drop in fasting blood glucose. Supports a genuine glycemic effect — but the authors framed it as 'modest,' and the analysis was limited to fasting glucose, not HbA1c or hard outcomes.
Only fasting glucose was pooled; no long-term glycemic or clinical endpoints. Effect magnitude is small and clinically modest.
Cochrane review — cinnamon for diabetes mellitus
Null · Systematic review
Leach & Kumar, 2012, Cochrane Database of Systematic Reviewsn=577The Cochrane review — the most conservative, methodologically strict synthesis — concluded there was insufficient evidence to support cinnamon for type 1 or type 2 diabetes. No significant effect on HbA1c, and the data on fasting glucose and lipids were too inconsistent to draw conclusions. The honest counterweight to the positive meta-analyses.
Cochrane's stricter inclusion and risk-of-bias standards partly explain why it is more negative than Allen 2013 or Davis 2011 — but that conservatism is exactly the point: the better-quality the synthesis, the weaker the effect looks.
Cinnamon, HbA1c & blood pressure in T2D (RCT)
positive · RCT
Akilen et al., 2010, Diabetic Medicinen=58A double-blind RCT where 2 g/day cinnamon for 12 weeks reduced HbA1c (8.22% → 7.86%) and both systolic and diastolic blood pressure versus placebo in poorly controlled T2D. One of the stronger individual positive trials — and one of the few showing an HbA1c effect, which most others do not.
Single-center, modest sample (n=58), and an HbA1c effect that conflicts with the null HbA1c finding in the larger Allen 2013 meta-analysis. An outlier as much as a confirmation.
Cinnamon improves glucose and lipids in T2D (RCT)
positive · RCT
Khan et al., 2003, Diabetes Caren=60The trial that launched the cinnamon-for-diabetes craze: reported large drops in fasting glucose (18–29%) and lipids at all three doses. Its dramatic effect sizes drove a generation of supplement marketing — but it has never been cleanly replicated, and its findings now carry a formal Expression of Concern.
In 2025 Diabetes Care issued an Expression of Concern citing statistical problems, including baseline group differences inconsistent with proper randomization. Treat its outsized effect sizes with strong skepticism.
Water-soluble cinnamon extract in prediabetes (CinnulinPF)
positive · RCT
Ziegenfuss et al., 2006, Journal of the International Society of Sports Nutritionn=22Industry-fundedA standardized water-soluble extract (Cinnulin PF®) lowered fasting glucose ~8.4% and systolic blood pressure ~3.8% in prediabetic/metabolic-syndrome adults over 12 weeks. The basis for low-dose 'cinnamon extract' supplements — water-soluble extraction removes the fat-soluble coumarin, a genuine safety advantage.
Small (n=22) and conducted by/with the extract's manufacturer (Cinnulin PF). Body-composition changes were tiny. Industry funding plus small sample warrants caution.
Cinnamon does not improve glycemic control (RCT, null)
Null · RCT
Vanschoonbeek et al., 2006, Journal of Nutritionn=25A clean negative trial: in postmenopausal women with T2D, 1.5 g/day cinnamon for 6 weeks produced NO improvement in fasting glucose, HbA1c, insulin sensitivity, or lipids versus placebo. The directly contradictory counterpoint to Khan 2003 and a key reason the literature is so heterogeneous.
Small (n=25) and a lower dose than some positive trials, but well-conducted and frequently cited as the archetypal cinnamon null result.
Blood pressure & cholesterol
Mechanism
Proposed vasodilatory and lipid-modulating effects of cinnamon polyphenols, plus secondary improvement from better glycemic control.
Some trials report modest reductions in blood pressure (Akilen 2010, Ziegenfuss 2006) and lipids (Allen 2013 meta-analysis), but the effects are small, inconsistent across studies, and largely seen in diabetic/metabolic-syndrome populations. The cardiovascular case is weaker than the glycemic one and rests on the same heterogeneous evidence base.
Signals are limited to cardiometabolically impaired adults and are too small and inconsistent to count on. Not a blood-pressure or cholesterol treatment.
Cinnamon, HbA1c & blood pressure in T2D (RCT)
positive · RCT
Akilen et al., 2010, Diabetic Medicinen=58A double-blind RCT where 2 g/day cinnamon for 12 weeks reduced HbA1c (8.22% → 7.86%) and both systolic and diastolic blood pressure versus placebo in poorly controlled T2D. One of the stronger individual positive trials — and one of the few showing an HbA1c effect, which most others do not.
Single-center, modest sample (n=58), and an HbA1c effect that conflicts with the null HbA1c finding in the larger Allen 2013 meta-analysis. An outlier as much as a confirmation.
Cinnamon in type 2 diabetes (updated meta-analysis)
mixed · Meta-analysis
Allen et al., 2013, Annals of Family Medicinen=543The most-cited cinnamon meta-analysis (10 RCTs, 543 people with T2D). Cinnamon lowered fasting plasma glucose (~−24.6 mg/dL) and improved lipids — but, crucially, did NOT significantly change HbA1c, the gold-standard marker of long-term glucose control. A statistically real fasting-glucose signal that may not translate to meaningful diabetes management.
High between-trial heterogeneity and varied cinnamon species/doses. The absence of an HbA1c effect undercuts the practical importance of the fasting-glucose drop.
Water-soluble cinnamon extract in prediabetes (CinnulinPF)
positive · RCT
Ziegenfuss et al., 2006, Journal of the International Society of Sports Nutritionn=22Industry-fundedA standardized water-soluble extract (Cinnulin PF®) lowered fasting glucose ~8.4% and systolic blood pressure ~3.8% in prediabetic/metabolic-syndrome adults over 12 weeks. The basis for low-dose 'cinnamon extract' supplements — water-soluble extraction removes the fat-soluble coumarin, a genuine safety advantage.
Small (n=22) and conducted by/with the extract's manufacturer (Cinnulin PF). Body-composition changes were tiny. Industry funding plus small sample warrants caution.
Weight & body composition
Mechanism
Hypothesized improvement in insulin sensitivity nudging body composition; no compelling mechanism for direct fat loss.
Essentially unsupported. The only body-composition signal comes from one small industry-funded extract trial (Ziegenfuss 2006) showing tiny changes (~0.7% body fat). There is no good evidence cinnamon causes meaningful weight or fat loss. Treat 'cinnamon for weight loss' as marketing.
No reliable evidence of a weight or fat-loss effect in any population.
Water-soluble cinnamon extract in prediabetes (CinnulinPF)
positive · RCT
Ziegenfuss et al., 2006, Journal of the International Society of Sports Nutritionn=22Industry-fundedA standardized water-soluble extract (Cinnulin PF®) lowered fasting glucose ~8.4% and systolic blood pressure ~3.8% in prediabetic/metabolic-syndrome adults over 12 weeks. The basis for low-dose 'cinnamon extract' supplements — water-soluble extraction removes the fat-soluble coumarin, a genuine safety advantage.
Small (n=22) and conducted by/with the extract's manufacturer (Cinnulin PF). Body-composition changes were tiny. Industry funding plus small sample warrants caution.
3 forms of Ceylon Cinnamon compared
Ceylon cinnamon (Cinnamomum verum)
Standard whole-bark powder; very low coumarin
Best forThe safer choice for daily supplementation'True cinnamon.' Coumarin content ranges from undetectable to ~300 mg/kg — far below cassia. For anyone taking cinnamon daily, Ceylon is the form that avoids the liver-toxicity concern. The trade-off: it's milder, more expensive, and most cheap supplements and supermarket cinnamon are NOT Ceylon.
Cassia cinnamon (Cinnamomum cassia / aromaticum)
Standard whole-bark powder; high coumarin
Best forThe common, cheap cinnamon — used in most trials and most supermarket productsThe dominant commercial cinnamon and the species in most glycemic trials, but it contains high coumarin (~1,700–7,670 mg/kg). Daily supplement doses can push smaller adults and children over the EFSA tolerable daily intake. Fine as an occasional spice; questionable as a daily high-dose supplement.
Cinnulin PF®
Water-soluble cinnamon extract (Cinnulin PF®)
Concentrated water-soluble extract; coumarin largely removed
Best forLow-dose standardized extract used in the prediabetes RCT (Ziegenfuss 2006)Water extraction concentrates the water-soluble polyphenols (type-A procyanidins) while leaving behind the fat-soluble coumarin — a genuine safety advantage over whole cassia powder. The catch: the supporting trial is small and manufacturer-funded.
metabolism250–500 mg
Are you deficient? Symptoms, risk groups, lab tests
Cinnamon is a spice, not an essential nutrient — there is no deficiency state. It is used as a supplement for potential metabolic effects, not to correct a shortfall.
Common symptoms
- Not applicable — cinnamon is not an essential nutrient and has no deficiency syndrome
Side effects and drug interactions
Side effects
Coumarin-related liver toxicity (cassia)
Uncommon · Cumulative coumarin above EFSA TDI of 0.1 mg/kg body weight/day
Cassia cinnamon contains coumarin, which is hepatotoxic and carcinogenic in animals and can cause idiosyncratic liver injury in susceptible people. Daily high-dose cassia supplements can exceed the tolerable daily intake, especially in smaller adults and children.
Worse with:cassia
Gentler:ceylon, cinnulin pf
Mouth or skin irritation
Uncommon
Cinnamaldehyde can cause oral mucosal irritation, mouth sores, or contact dermatitis in sensitive individuals, particularly with concentrated products or cinnamon oil.
Hypoglycemia risk with diabetes medication
Uncommon
Because cinnamon may lower blood glucose, combining it with glucose-lowering drugs could theoretically additively lower blood sugar.
Drug interactions
Additive effect
metforminsulfonylureasinsulinCinnamon's modest glucose-lowering effect may be additive with antidiabetic medication, theoretically increasing hypoglycemia risk.
If you take glucose-lowering medication, monitor blood sugar when starting cinnamon and discuss with your prescriber. Do not use cinnamon as a substitute for prescribed diabetes treatment.
Combined-effect risk
hepatotoxic drugshigh-dose acetaminophenstatinsmethotrexateCoumarin in cassia cinnamon adds to total liver burden; combining daily high-dose cassia with other hepatically-stressing drugs may compound risk.
Avoid daily high-dose cassia cinnamon if you have liver disease or take hepatotoxic medications. Use low-coumarin Ceylon instead.
Additive effect
warfarinanticoagulantsCoumarin is structurally related to (but distinct from) anticoagulant coumarins; very high cassia intake has been linked to anecdotal bleeding-risk concerns, though this is not well established at culinary doses.
People on warfarin should avoid large daily cassia-cinnamon supplement doses and keep intake consistent; discuss with a prescriber.
Other critical caveats
- Cassia cinnamon — the cheap, common type in most supermarket spice and capsule products — contains coumarin, a hepatotoxin. Daily supplement doses can exceed the EFSA tolerable daily intake (0.1 mg/kg/day), especially in smaller adults and children. For daily use, choose Ceylon (Cinnamomum verum), which is very low in coumarin.
- Even the positive meta-analyses are unimpressive where it counts: Allen 2013 found a fasting-glucose drop but NO change in HbA1c, the marker of long-term glucose control. The Cochrane review (Leach 2012) concluded there is insufficient evidence to recommend cinnamon for diabetes at all.
- The famous Khan 2003 trial that started the cinnamon-for-diabetes trend now carries a 2025 Expression of Concern from Diabetes Care over statistical and randomization problems. Its dramatic effect sizes have never been cleanly replicated.
- Cinnamon is not a diabetes treatment and not a substitute for medication. Any benefit is small, inconsistent, and limited to people with type 2 diabetes or metabolic syndrome — not healthy adults or weight-loss seekers.
Frequently asked
Does cinnamon actually lower blood sugar?
Modestly and inconsistently, and mainly in people who already have type 2 diabetes. Meta-analyses show a small drop in fasting glucose (Allen 2013, Davis 2011), but even the positive ones found no change in HbA1c — the marker of long-term control — and the Cochrane review concluded there's insufficient evidence to recommend it. Several well-run trials show no effect at all. It is not a replacement for diabetes medication.Is cinnamon safe to take every day?
It depends on the type. Cassia cinnamon — the common, cheap variety — contains coumarin, which is hepatotoxic and can exceed the safe daily intake at supplement doses, especially in smaller people. If you take cinnamon daily, use Ceylon (Cinnamomum verum), which is very low in coumarin, or a water-soluble extract (like Cinnulin PF) that removes most of it.What's the difference between Ceylon and cassia cinnamon?
Ceylon ('true cinnamon,' Cinnamomum verum) is mild, more expensive, and very low in coumarin. Cassia is cheaper, stronger-flavored, the type in most supermarkets and supplements — and high in coumarin (roughly 1,700–7,670 mg/kg versus often undetectable in Ceylon). For occasional cooking either is fine; for daily supplementation, Ceylon is the safer choice.How much cinnamon should I take?
Trials have used anywhere from 250–500 mg/day of concentrated extract up to 1–6 g/day of whole powder. There's no established effective dose because the evidence is so inconsistent. If you try it, favor a low-coumarin form (Ceylon or a water-soluble extract), keep expectations modest, and don't use it in place of prescribed treatment.Will cinnamon help me lose weight?
There's no good evidence it does. The only body-composition signal comes from a single small, industry-funded extract trial showing a tiny change. 'Cinnamon for weight loss' is marketing, not science — any metabolic effect is small and limited to people with diabetes or metabolic syndrome.
References
- 01Examine.com — Cinnamon
- 02Allen et al., 2013 — Cinnamon in type 2 diabetes meta-analysis (Ann Fam Med)
- 03Leach & Kumar, 2012 — Cinnamon for diabetes mellitus (Cochrane)
- 04Vanschoonbeek et al., 2006 — Null glycemic RCT (J Nutr)
- 05German BfR — Cassia cinnamon and coumarin consumer safety guidance
Last reviewed2026-05-24