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Cinnamon (Cinnamomum spp.): A Comprehensive Reference

1. Identity: Botanical Classification, Natural Sources, and Commercial Forms

Botanical Classification

Cinnamon is a spice obtained from the inner bark of several tree species from the genus Cinnamomum, all members of the family Lauraceae. Cinnamomum verum (alternatively C. zeylanicum), known as "Ceylon cinnamon" after its origins in Sri Lanka (formerly Ceylon), is considered to be "true cinnamon," but most cinnamon in international commerce is derived from four other species, usually referred to as "cassia": C. burmannii (Indonesian cinnamon or Padang cassia), C. cassia (Chinese cinnamon or Chinese cassia), C. loureiroi (Saigon cinnamon or Vietnamese cassia), and the less common C. citriodorum (Malabar cinnamon).

Cinnamomum verum, known as the "true cinnamon tree" and "Ceylon cinnamon tree," is an evergreen small tree belonging to the Lauraceae family. Cinnamomum verum is native to India, Sri Lanka, Bangladesh, and Myanmar. Cinnamomum cassia, also called "Chinese cinnamon," is an evergreen tree native to South China; Chinese cinnamon is produced mainly in the southern regions and is also widely grown in other areas of South and East Asia.

Both cinnamons have older scientific names: Cinnamomum zeylanicum is now properly called Cinnamomum verum, and Cinnamomum aromaticum is an older (superseded) name for Cinnamomum cassia. In both trade and clinical research, "cinnamon" can refer to different species and product forms, so results from one study may not match what you buy.

Global Production

In 2023, world production of cinnamon was 238,403 tonnes; four countries accounted for 98% of this total: China, Vietnam, Indonesia, and Sri Lanka.

Physical Distinctions Between Species

Among cassia, Chinese cinnamon is generally medium to light reddish-brown, hard and woody in texture, and thicker (2–3 mm thick), as all of the layers of bark are used. Ceylon cinnamon, using only the thin inner bark, has a lighter brown colour and a finer, less dense, and more crumbly texture. It is subtle and more aromatic in flavour than cassia, and it loses much of its flavour during cooking. Ceylon cinnamon sticks (quills) have many thin layers and can easily be made into powder, whereas cassia sticks are much harder.

Common Forms and Preparations

Cinnamon is used in cooking as either entire quills (or broken pieces thereof), or as the dried ground spice. The essential oil extracted from the dried inner bark of the cinnamon plant has long been used as a flavouring agent in foods, beverages, candies, and chewing gums. As a dietary supplement, it is commercially available in several distinct forms:

• Whole quills or sticks: The inner bark is loosened by being rubbed with a brass rod, then split and peeled off. Long, full quills of cinnamon are more valuable than broken pieces. These quills are then dried over several days in the shade, then in darkness.
• Ground powder: Ground cinnamon is produced by harvesting cinnamon bark, drying it, and milling it into a fine powder.
• Essential oil: Twigs, leaves, and berries are crushed to make cinnamon oil.
• Encapsulated/standardized extracts: Cinnamon ranked within the 30 top-selling herbal supplements in 2020. Standardized water-soluble extracts — notably those traded under names such as Cinnulin PF® — are common supplement forms studied in clinical trials.

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2. Traditional and Historical Use

Ancient and Classical Civilizations

Cinnamon is one of the oldest spices recorded in human history. Its origins lie in South Asia, specifically in Sri Lanka and southern India, where it grows naturally in tropical forests. Its use dates back as early as 2000 BC, when it formed part of trade networks linking Asia, the Middle East, and Africa. Cinnamon is mentioned repeatedly in both the Old Testament (in the book of Exodus and The Song of Songs) and in Sanskrit writings. Cinnamon was used medicinally as well as as a flavouring agent, and in embalming in ancient Egypt, its use attributable to the spice's antibacterial properties.

Cinnamon was so highly prized among ancient nations that it was regarded as a gift fit for monarchs and even for a deity; an inscription records the gift of cinnamon and cassia to the temple of Apollo at Miletus. Its source was kept a trade secret in the Mediterranean world for centuries by those in the spice trade, to protect their monopoly as suppliers. In Ancient Rome, it was regarded as a luxury commodity, more valuable even than gold, reserved for the elite and employed in perfumes, ointments, and medicinal preparations.

As a spice, mention of cinnamon dates back to Chinese writings from 4000 BC. Cassia cinnamon has been used in Chinese medicine since at least 2700 BCE. It is one of the oldest recorded medicinal herbs in the Shennong Ben Cao Jing, an ancient Chinese pharmacopeia. Cassia cinnamon was used to treat colds, boost circulation, and improve digestion — uses that continue in Traditional Chinese Medicine today.

Traditional Chinese Medicine (TCM)

In Traditional Chinese Medicine (TCM), cinnamon — particularly the Cassia variety — is known as Rou Gui (the bark) and Gui Zhi (the young twigs). For centuries, it has held a prominent place among the group of herbs that warm and mobilise the body's vital energy, known as Qi. According to this ancient therapeutic approach, cinnamon supports energetic functions linked to internal warmth, circulation, and the body's overall balance.

Ayurvedic Medicine

In the ancient system of Ayurveda, cinnamon was revered not only for its delightful flavour but also for its powerful medicinal properties. Known as "Twak," cinnamon played a vital role in this holistic approach to well-being. Ayurvedic practitioners recognized its warming nature, which made it a valuable ingredient for balancing the body's doshas, particularly Vata and Kapha. Cinnamon was employed to aid digestion, alleviate respiratory ailments, and address menstrual discomfort.

Medieval and Islamic Medicine

The 10th-century Persian physician Avicenna (Ibn Sina) included cinnamon in his famous medical texts, noting its warming properties and effectiveness in treating colds, coughs, and inflammation. It was not until the Age of Discovery, when the Portuguese arrived in Sri Lanka in the 16th century, that Europe gained direct access to cinnamon plantations.

German Commission E Recognition

Most therapeutic uses of Chinese cinnamon bark are rooted in its historical use as a traditional medicine and on laboratory and animal studies. German health authorities (Commission E) approve of cinnamon bark for mild gastrointestinal spasms, stimulating appetite, and relieving indigestion.

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3. Key Constituents and Active Compounds

Volatile Phenylpropanoids

The characteristic aroma and flavour of cinnamon derive from its essential oil and principal component, cinnamaldehyde, as well as numerous other constituents including eugenol. The main active components of cinnamon oil include cinnamaldehyde, cinnamic acid, and eugenol, which play key roles in its pharmacological effects.

• Cinnamaldehyde (trans-cinnamaldehyde): Cinnamon contains the abundant component cinnamaldehyde, a phenylpropanoid that produces the flavour and scent of cinnamon. It is the predominant constituent of the essential oil and is central to most proposed pharmacological mechanisms.
• Eugenol: Eugenol is a major compound in Ceylon cinnamon but not in Cassia cinnamon, making it a characteristic biomarker for distinguishing between different cinnamon species.
• Cinnamic acid: A phenolic acid that contributes to antioxidant and anti-inflammatory activity.

Polyphenolic Compounds

Cinnamon bark contains water-soluble polyphenolic polymers, including procyanidins (type A proanthocyanidins) and catechins. A specific polyphenol termed MHCP (methyl hydroxychalcone polymer) was isolated from cinnamon and reported to exhibit insulin-mimetic activity in adipocytes. These include catechin-based structures and procyanidin B and A-type linkages of polyphenolic compounds, resulting in a large variety of polyphenol-based components.

Coumarin

Coumarin (2H-chromen-2-one) is an aromatic compound found in several plants in nature, including the cinnamon plant species. Coumarin has a characteristically sweet odour and a bitter taste, and is an established hepatotoxin and carcinogen when consumed in large amounts. Due to the variable amount of coumarin in C. cassia — usually well over 1 mg of coumarin per gram of cinnamon and sometimes up to 12 times that — C. cassia has a low safe-intake-level upper limit to adhere to the tolerable daily intake. In contrast, C. verum has only trace amounts of coumarin.

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4. Established Mechanisms of Action

Insulin Signalling and Glucose Metabolism

Beneficial effects of cinnamon on metabolic and cardiovascular health can be related to multiple molecular mechanisms attributed to its bioactive compounds, primarily cinnamaldehyde, cinnamic acid, and polyphenols. One key mechanism is enhancement of insulin sensitivity and regulation of glucose metabolism by cinnamon. Cinnamaldehyde can activate insulin receptors and promote glucose transporter 4 (GLUT4) translocation in muscle and fat tissues, facilitating greater glucose uptake. Moreover, cinnamon activates the phosphorylation process in insulin signalling cascade, leading to the activation of intracellular cascade events.

Cinnamon polyphenols can activate insulin receptor autophosphorylation and glucose uptake in cells, potentially through affecting the cell surface insulin receptor or downstream signalling. Polyphenols can also bind to cell membranes or membrane proteins, altering their conformation or clustering. Procyanidin oligomers might interact with lipid rafts and influence insulin receptor localisation, thereby enhancing insulin signalling sensitivity.

A cinnamon extract affects a tyrosine phosphatase that would otherwise inactivate the insulin receptor, and a water extract of cinnamon increased insulin-dependent GLUT4. Water-soluble cinnamon polyphenols also inhibited glucose production, accompanied by decreased expression of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, major regulators of hepatic gluconeogenesis.

Another possible mechanism that explains the hypoglycaemic effect of cinnamon is an increase in the expression of peroxisome proliferator-activated receptor (PPAR) alpha and gamma receptors, thereby increasing insulin sensitivity. Studies also showed that cinnamon administration increases the level of glucagon-like peptide 1 (GLP-1).

Lipid-Lowering Mechanisms

The lipid-lowering effects of cinnamon are mediated through multiple mechanisms. Cinnamon inhibits hepatic HMG-CoA reductase activity, thereby reducing endogenous cholesterol synthesis. It also promotes lipolysis, potentially by improving insulin resistance and suppressing the overproduction of intestinal apoB48-containing lipoproteins, contributing to lipid metabolism regulation. Moreover, cinnamon is rich in polyphenolic compounds, which inhibit intestinal cholesterol absorption and upregulate the expression of peroxisome proliferator-activated receptor alpha (PPAR-α) in adipose tissue, leading to enhanced lipoprotein lipase activity and improved uptake and metabolism of free fatty acids.

Antimicrobial Mechanisms

Cinnamon's mechanisms of action with respect to antimicrobial activity include disrupting cell membranes, inhibiting ATPase activity, and preventing biofilm formation. The main chemical constituents of C. cassia and C. verum natural oils — eugenol and cinnamaldehyde — can inhibit microbial growth.

Anti-Inflammatory Mechanisms

Cinnamon oil's anti-inflammatory properties are evidenced by its ability to suppress inflammatory markers like vascular cell adhesion molecules and macrophage colony-stimulating factors. Nuclear Factor Kappa B (NF-κB) functions as a transcription factor that is stress sensitive. Endogenous levels of NF-κB regulate transcription in response to the stress stimulus, including those from tumour necrosis factor alpha (TNFα), reactive oxygen species, inflammatory factors, and infection. Nuclear factor erythroid related factor 2 (Nrf2) has been indicated to affect cancer progression and potentially provide preventative measures, and various cinnamon derivatives target Nrf2.

Ion Channel and GPCR Modulation

Cinnamon-derived phytonutrients, particularly cinnamaldehyde, eugenol, and polyphenolic compounds, modulate key ion channels and GPCR pathways involved in metabolic regulation. The membrane interactions of cinnamon's phytochemicals are governed by their lipophilicity. Cinnamaldehyde and eugenol are highly lipophilic and readily diffuse across cell membranes, enabling direct access to hydrophobic pockets on ion channels/GPCRs, and they can also embed in the lipid bilayer and alter membrane fluidity, which might indirectly affect membrane protein conformation.

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5. Scientific Evidence by Area of Use

5.1 Glycaemic Control and Type 2 Diabetes

This is the most extensively studied area of cinnamon research, though the overall evidence base remains mixed, with significant heterogeneity across trials.

The NCCIH does not recognize the use of cinnamon for either the treatment or prevention of diabetes or other disease. Neither the American Diabetes Association (Grade C evidence level) nor the Canadian Diabetes Association (Grade D evidence level) endorse its use. Cinnamon has been suggested to help patients with type 2 diabetes mellitus achieve better glycaemic control, although conclusions from meta-analyses are mixed.

Data from clinical trials have shown conflicting results on the effectiveness of cinnamon for diabetes. A 2012 Cochrane systematic review of 10 randomized controlled trials involving a total of 577 participants found insufficient evidence to support the use of cinnamon for type 1 or type 2 diabetes.

More recent pooled analyses have found more favourable, though still mixed, signals. Sixteen randomized controlled studies were included in one meta-analysis. Cinnamon significantly reduced fasting blood glucose (FBG) and homeostatic model assessment for insulin resistance (HOMA-IR) compared to placebo, with a weighted mean difference (WMD) of −0.545 (95% CI: −0.910, −0.18) mmol/L and −0.714 (−1.388, −0.04), respectively. There was no significant change in HbA1c or lipid profiles. The conclusion was that cinnamon reduced FBG and HOMA-IR in T2DM and pre-diabetes patients compared to placebo, but high heterogeneity observed among included studies warrants further clinical trials after standardisation of cinnamon formulation.

An umbrella meta-analysis published in PMC (2023), pooling 11 prior meta-analyses of RCTs, found the following: Cinnamon supplementation was effective in reducing serum FPG (WMD: −10.93 mg/dL; 95% CI: −16.22, −5.65), insulin (WMD: −2.01 IU/mL; 95% CI: −3.96, −0.07), HOMA-IR levels (WMD: −0.61; 95% CI: −0.91, −0.31), and HbA1c (WMD: −0.10%; 95% CI: −0.17, −0.03).

A dose–response meta-analysis (published 2023, covering literature up to November 2022) noted: A daily intake of cinnamon of less than 1200 mg can effectively reduce fasting blood glucose levels, which is considered an appropriate intervention dose.

A separate 2019 meta-analysis of 18 studies found: Supplementation with cinnamon reduced FBS by −19.26 mg/dL (95% CI: −28.08, −10.45; I²: 96.5%; p = 0.0001) compared to placebo. Supplementation with cinnamon can reduce serum levels of glucose with no changes in other glycaemic parameters and anthropometric indices. However, due to high heterogeneity, findings should be interpreted with great caution.

Overall evidence strength for glycaemic control: Moderate in quantity but limited in quality. Statistically significant reductions in fasting glucose are frequently reported, but the clinical magnitude is modest, heterogeneity is high, and effects on HbA1c are inconsistent. Neither the American Diabetes Association, the Canadian Diabetes Association, nor the NCCIH currently endorse cinnamon for diabetes treatment.

5.2 Lipid Profile (Dyslipidaemia)

A 2020 systematic review and meta-analysis of 16 studies, along with another 2020 review and meta-analysis with 9 studies conducted by the same research group, found that cinnamon supplementation in patients with type 2 diabetes may cause a decrease in triglycerides, total cholesterol, LDL, and blood pressure compared to placebo.

A 2024 systematic review and meta-analysis covering literature up to November 2023 found mixed results depending on dose: The meta-analysis on the impact of cinnamon on lipid profiles indicates a non-significant overall effect on LDL (WMD, −2.48; 95% CI, −9.70, 4.72), though significant reductions are seen with doses <500 mg/day (−10.26). The overall effect on HDL is non-significant (WMD, 3.97), showing varying responses at different doses. Triglycerides exhibit a significant overall reduction (WMD, −6.88; 95% CI, −12.62, −1.15), particularly in the <500 mg/day group. The overall effect on total cholesterol is non-significant.

An umbrella meta-analysis of eleven prior meta-analyses (data to January 2022) reported: Cinnamon consumption can significantly improve total cholesterol (WMD = −1.01 mg/dL; 95% CI: −2.02, −0.00, p = 0.049), LDL-C (WMD = −0.82 mg/dL; 95% CI: −1.57, −0.07, p = 0.032), and HDL-C (WMD = 0.47 mg/dL; 95% CI: 0.17, 0.77, p = 0.002) levels, but not triglyceride levels.

Overall evidence strength for lipid effects: Effects on triglycerides appear more consistent than effects on LDL or total cholesterol. Results across meta-analyses are conflicting — different meta-analyses reach opposite conclusions on the same outcomes — likely reflecting differences in included populations, species of cinnamon, doses, and study duration. Evidence is preliminary.

5.3 Cardiovascular Risk Factors and Blood Pressure

An umbrella review of meta-analyses found that cinnamon supplementation is significantly associated with improvements in fasting blood glucose and lipid profiles, with more pronounced effects observed in patients with diabetes and metabolic syndrome. Subgroup analyses suggest that higher doses (>1.5 g/day) and shorter intervention durations (≤2 months) may enhance these benefits. Additionally, cinnamon shows potential in modulating insulin resistance, antioxidant capacity, and blood pressure regulation.

A 2025 systematic review and meta-analysis of 49 studies (covering data through July 2024) noted: Significant reductions were observed in waist circumference, blood pressure, fasting glucose, and lipid profiles, along with improvements in inflammatory markers and oxidative stress parameters, underscoring cinnamon's potential as a complementary approach.

Overall evidence strength for cardiovascular effects: Preliminary. Numerous meta-analyses show modest, statistically significant reductions in various cardiovascular risk markers, but clinical significance is uncertain and findings are heavily qualified by high heterogeneity and inconsistent results across individual trials.

5.4 Anti-Inflammatory Activity

The results from available evidence reveal that cinnamon improved glycaemic and lipidaemic indicators. Clinical trials also clarified that cinnamon possesses an anti-inflammatory effect, which may act beneficially in diabetes.

Overall evidence strength for anti-inflammatory effects: Largely preclinical (in vitro and animal studies). Some clinical trial data in diabetic populations suggest reductions in markers such as CRP, but the evidence is not yet sufficient to draw firm conclusions.

5.5 Antimicrobial Activity

In vitro studies show higher activity of cinnamon against Gram-positive (Enterococcus, Streptococcus, Staphylococcus) and Gram-negative (Pseudomonas aeruginosa) bacteria strains. These results are consistent with findings revealing that bark oil of cinnamon completely inhibited the growth of selected Gram-negative and Gram-positive bacteria.

Overall evidence strength for antimicrobial effects: Primarily in vitro. Robust human clinical trial data on antimicrobial applications are lacking. In vitro evidence is supportive but does not directly translate to clinical efficacy in humans.

5.6 Polycystic Ovary Syndrome (PCOS)

Cinnamon supplementation demonstrates promising effects on body weight, blood sugar, total cholesterol, LDL, and insulin resistance in women with PCOS, indicating its potential in mitigating cardiovascular risk factors associated with this condition. This is an emerging area of research with relatively few, small-scale trials.

Overall evidence strength for PCOS: Preliminary. Available data are from small, short-duration RCTs with limited power.

5.7 Body Weight and Composition

Cinnamon products are promoted as a dietary supplement for diabetes and weight loss. A 2020 systematic review and meta-analysis of controlled clinical trials (referenced by NCCIH) investigated body weight effects. A few dietary supplements, such as chromium, cinnamon, or berberine, might help improve blood sugar control. However, the research is not strong enough to allow definite conclusions to be reached about their effects.

Overall evidence strength for weight/body composition: Weak. Findings are inconsistent, and any effects observed are modest. The current literature does not support cinnamon as an effective weight-loss agent.

5.8 Neuroprotective and Alzheimer's Disease Research

A cinnamon extract promotes complete disassembly of recombinant tau filaments and causes substantial alteration of the morphology of paired-helical filaments isolated from brains of those with Alzheimer's disease, without being deleterious to the normal cellular function of tau. An A-linked proanthocyanidin trimer molecule isolated from Ceylon cinnamon extract has shown to contain a significant proportion of this inhibitory activity.

Overall evidence strength for neuroprotective effects: Early-stage and primarily preclinical. No human clinical trials have been completed demonstrating clinical benefit for Alzheimer's disease or cognitive function.

5.9 Cancer — Preclinical Research Only

An important active compound within cinnamon is eugenol, which induces apoptosis in promyelocytic leukaemia cells (HL60). It also increases reactive oxygen species (ROS) within colon cancer, suggesting it as a potential alternative treatment option. Cinnamaldehyde also shows evidence of inducing apoptosis for HL60; at high concentrations it upregulates CD95 expression and PARP cleavage, while at low concentrations it induces apoptosis by upregulating caspase-8 activity, Bax, and Bid and decreasing anti-apoptotic proteins.

Cinnamon components have been tied to cancer prevention by positively affecting the gut microbiome and inhibiting inflammation. However, this line of research concludes with a recognition of the need for clinical studies and potential risk associated with cinnamon intake.

Overall evidence strength for anticancer effects: Purely preclinical (cell-line and animal studies). No human clinical trials have been conducted. This evidence cannot be extrapolated to clinical benefit in humans.

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6. Dosage Forms and Dosages Reported in Clinical Studies

Dosages used in published human studies have varied widely, which is a major source of heterogeneity in the literature. The following are ranges specifically reported in the sources referenced here:

• Powdered cinnamon bark (whole): Studies have used doses ranging from 120 mg to 6 grams per day. Studies are heterogeneous with varying doses from 120 mg to 6 grams.
• Doses commonly associated with glycaemic benefit: A daily intake of cinnamon of less than 1200 mg was identified as an appropriate intervention dose for reducing fasting blood glucose levels. Another review covering 28 studies on patients with T2DM reported significant improvements in FBG, HbA1c, and HOMA-IR with doses of 2 g/day or more.
• Doses associated with lipid effects: Significant reductions in LDL and triglycerides were seen particularly at doses <500 mg/day.
• Subgroup findings on dose and duration: Subgroup analyses suggest that higher doses (>1.5 g/day) and shorter intervention durations (≤2 months) may enhance metabolic benefits.

Important caveat: Dose equivalence is complicated by the lack of standardisation — studies use different cinnamon species, whole powder, water-soluble extracts, or oil, and rarely specify species rigorously. Results from one dose or preparation cannot reliably be generalised across products.

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7. Safety Considerations

7.1 Coumarin Content and Hepatotoxicity Risk

The most well-documented safety issue with cinnamon supplements, particularly from Cassia species, is coumarin content. Cassia cinnamon, the most common type of cinnamon sold in the United States and Canada, contains varying amounts of coumarin, a substance that may cause or worsen liver disease if large amounts are ingested.

Coumarin has a characteristically sweet odour and a bitter taste, and is an established hepatotoxin and carcinogen when consumed in large amounts. The tolerable daily intake has been defined as 0.1 mg coumarin per kg body weight according to the European Food Safety Authority (EFSA) and the German Institute for Risk Assessment (BfR).

Ceylon cinnamon contains only minimal amounts of coumarin. Cassia cinnamon, on the other hand, can contain over 1000 mg/kg of coumarin. Coumarin is a flavouring substance contained in relatively high concentrations in cinnamon varieties collectively known as "Cassia cinnamon." In especially sensitive persons, even comparatively small quantities of coumarin can cause liver damage, although the effect is usually reversible.

In 2004, the European Food Safety Authority (EFSA) concluded that the carcinogenic effect of coumarin was not caused by a genotoxic mechanism, and a tolerable daily intake (TDI) of 0.1 mg coumarin/kg bodyweight, based on a no-observed-adverse-effect level (NOAEL) for liver toxicity in a two-year dog study, was established. EFSA further concluded that exposure to coumarin resulting in an intake three times higher than the TDI for one to two weeks is not of safety concern.

To avoid exceeding the TDI set by EFSA, the French food safety agency ANSES recommends keeping coumarin intake through food supplements below 4.8 mg per day for a 60 kg adult. It also advises people with a history of liver disease to avoid consumption of cinnamon-rich foods and food supplements containing coumarin.

Consumers who take cinnamon-based food supplements should be aware that such products may contain high quantities of Cassia cinnamon.

7.2 Species-Specific Coumarin Levels

In one analysis, authentic Ceylon cinnamon bark contained 12–143 mg/kg of coumarin — a phenolic typically low in true cinnamon — but market samples contained coumarin at levels as high as 3462 mg/kg, indicating probable contamination with cassia in counterfeit cinnamon.

Coumarin was at first suspected to have genotoxic and carcinogenic effects in humans, but new toxicological data have shown it to be nongenotoxic and made it possible to define a tolerable daily intake. It is believed that most humans possess a major pathway for the metabolism of coumarin (the 7-hydroxycoumarin pathway) that differs from that in rats (the 3,4-coumarin epoxidation pathway) in which a reactive epoxide is formed. The 3,4-coumarin epoxide route has been linked to the hepatotoxicity and carcinogenic effects of coumarin observed in long-term studies in rats and mice.

7.3 Lead Contamination (Adulteration)

In March 2024, the US Food and Drug Administration recommended a voluntary recall on six brands of cinnamon applesauce due to extreme contamination with lead, after an investigation stemming from 500 reports of child lead poisoning across the US. The FDA determined that cinnamon (in applesauce pouches manufactured by AUSTROFOOD S.A.S. with cinnamon from Negasmart, both of Ecuador) was adulterated with lead chromate. The two suppliers are now Red Listed to forestall future adulteration.

7.4 Drug Interactions

Cinnamon, especially at supplemental doses, has demonstrated potential for pharmacokinetic drug interactions via cytochrome P450 (CYP450) enzyme pathways.

Cinnamon extracts have been shown to inhibit multiple cytochrome P450 enzymes (CYP1A2, 2C9, 2D6, 3A4), potentially affecting metabolism of blood thinners and other medications.

An NCCIH-funded clinical trial at Washington State University specifically evaluated cinnamon as a precipitant of pharmacokinetic interactions with CYP2A6 drug substrates in healthy volunteers. Nicotine gum was used as the CYP2A6 probe drug (positive control) and letrozole as a high-impact object drug. Results are intended to inform future research on the potential use of cinnamon as a smoking cessation agent, as well as the clinical impact on pharmacotherapeutic regimens involving letrozole in cancer patients.

Higher doses, such as concentrated supplements or oils, can activate a liver receptor called PXR, which plays a role in how the body breaks down many medications, meaning that cinnamon — especially in stronger forms — could affect how some drugs are metabolised.

Cinnamomum cassia (the most commonly used species) contains high levels of coumarin, which has anticoagulant properties and may interact with warfarin. Cinnamon has mild blood-thinning properties, which, combined with the effects of coumarin, further increases its potential to affect anticoagulant medications.

Little is known about whether it is safe to use Ceylon or cassia cinnamon in larger amounts as a medicine over the long term.

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8. Regulatory and Institutional Positions

• NCCIH (USA): The NCCIH does not recognize the use of cinnamon for either the treatment or prevention of diabetes or other disease. Data from clinical trials have shown conflicting results on the effectiveness of cinnamon for diabetes.
• German Commission E: German health authorities (Commission E) approve of cinnamon bark for mild gastrointestinal spasms, stimulating appetite, and relieving indigestion.
• EFSA / BfR (Europe): The European Food Safety Authority (EFSA) and the Federal Institute for Risk Assessment (BfR) recommend a tolerable daily intake (TDI) of 0.1 mg of coumarin per kilogram of body weight. For cinnamon-containing foods, new maximum permissible coumarin levels have been in place in the European Union since 2011.
• American and Canadian Diabetes Associations: The American Diabetes Association assigns Grade C evidence level for use of cinnamon for treatment of diabetes; the Canadian Diabetes Association assigns Grade D evidence level and has concluded that it is premature to recommend cinnamon for widespread use, but that it merits consideration for further research.

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References

• National Center for Complementary and Integrative Health (NCCIH) — Cinnamon: Usefulness and Safety
• NCCIH — Type 2 Diabetes and Dietary Supplements: What the Science Says
• NCCIH — 5 Things To Know About Type 2 Diabetes and Dietary Supplements
• Costello et al. — Do Cinnamon Supplements Have a Role in Glycemic Control in Type 2 Diabetes? A Narrative Review (PMC)
• Umbrella Meta-Analysis: The Effect of Cinnamon Supplementation on Glycemic Control in T2D or PCOS (PMC, 2023)
• Deyno et al. — Efficacy and Safety of Cinnamon in Type 2 Diabetes and Pre-Diabetes: A Meta-Analysis (PubMed, 2019)
• Namazi et al. — Impact of Cinnamon on Anthropometric Indices and Glycemic Status in T2DM: A Systematic Review and Meta-Analysis (PubMed, 2019)
• Zhou et al. — Efficacy of Cinnamon Supplementation on Glycolipid Metabolism in T2DM: A Meta-Analysis (PMC, 2022)
• Yu et al. — The Effect of Cinnamon on Glycolipid Metabolism: A Dose–Response Meta-Analysis of RCTs (MDPI Nutrients, 2023)
• Fateh et al. — Effects of Cinnamon Supplementation on Lipid Profile: Systematic Review and Meta-Analysis of RCTs (PMC, 2024)
• Umbrella Review: The Effects of Cinnamon on Patients with Metabolic Diseases — Meta-Analyses of RCTs (PMC, 2025)
• Systematic Review and Dose–Response Meta-Analysis: Cinnamon Supplementation on Cardiovascular Risk Factors (PMC, 2025)
• Sarmadi et al. — Cinnamon Consumption on Lipid Profile, Oxidative Stress, and Inflammation Biomarkers: Umbrella Meta-Analysis (Nutrition, Metabolism and Cardiovascular Diseases, 2023)
• Mehta et al. — Cinnamomum Species: Bridging Phytochemistry, Pharmacological Properties and Toxicological Safety (PMC, 2021)
• Cinnamon-Derived Phytonutrients as Modulators of Ion Channels and GPCR Signaling in Metabolic Diseases (PMC, 2025)
• Therapeutic Potential of Cinnamon Oil: Chemical Composition, Pharmacological Actions, and Applications (PMC, 2024)
• Ranasinghe et al. — Medicinal Properties of 'True' Cinnamon (Cinnamomum zeylanicum): A Systematic Review (PMC)
• Cinnamon Extract Lowers Glucose, Insulin and Cholesterol in People with Elevated Serum Glucose (PMC)
• Cinnamon: Potential Role in the Prevention of Insulin Resistance, Metabolic Syndrome, and Type 2 Diabetes (PMC)
• Prospective Nutraceutical Effects of Cinnamon Derivatives Against Insulin Resistance in Type II Diabetes Mellitus (PMC, 2023)
• Potential Effects of Cinnamon on Cancer Prevention and Progression (PMC/Frontiers in Nutrition, 2025)
• Cinnamon as a Complementary Therapeutic Approach for Dysglycemia and Dyslipidemia in T2DM: Molecular Mechanism Review (PMC, 2022)
• Cinnamon — Wikipedia (for general botanical and historical context)
• Cinnamon: The Historic Spice, Medicinal Uses, and Flavour Chemistry (ScienceDirect, 2023)
• Differentiation of the Four Major Species of Cinnamons Using FIMS (Journal of Agricultural and Food Chemistry, ACS)
• German Federal Institute for Risk Assessment (BfR) — FAQ on Coumarin in Cinnamon and Other Foods
• ANSES (French Food Safety Agency) — Beware of Overconsumption of Herbal Supplements Containing Coumarin
• Ole G. Størsrud et al. — Risk Assessment of Coumarin Using the Benchmark Dose Approach (Food and Chemical Toxicology, 2012)
• Blahová & Svobodová — Assessment of Coumarin Levels in Ground Cinnamon Available in the Czech Retail Market (PMC, 2012)
• ClinicalTrials.gov — Evaluating the Pharmacokinetics and Drug Interaction Potential of the Botanical Dietary Supplement Cinnamon (Washington State University / NCCIH)