Cinnamon

EVIDENCE: WEAK

Also sold as: Cinnamomum verum (Ceylon), Cinnamomum cassia, cinnamaldehyde, cassia

Cinnamon compounds have antimicrobial activity, and a small chewing-gum study measured reduced S. mutans. Blood-sugar studies have mixed results. Species and amount matter: cassia cinnamon contains coumarin, which can affect the liver with sustained exposure.

Compiled by iSupplementReviews editorial team ·Updated 2026-10-06 · 4 sources

Type: Botanical bark (culinary/medicinal)
Studied dose: Oral-pathogen data: cinnamon gum rinses over weeks; glycemic trials 1–6 g/day cassia powder
Best form: Ceylon cinnamon for chronic oral use (coumarin-light); label lists 'Cinnamon' — species and dose unnamed
Upper limit: No established upper intake limit for Ceylon; cassia's coumarin has a tolerable daily intake ~0.1 mg/kg/day — chronic heavy cassia use is a documented hepatotoxicity pattern
Our rating: WEAK — Mostly small, animal, or traditional evidence

What is cinnamon?

Cinnamon is the inner bark of Cinnamomum trees, used as a spice and flavoring. Cinnamaldehyde has antimicrobial activity. Human blood-sugar trials are inconsistent, while the small dental trial involved chewing gum rather than swallowed powder.

What does the research show?

Claim	Evidence	Dose studied	Verdict
Reduces oral S. mutans	One human chewing-gum study	Gum chewed daily, weeks	Weak-positive
Blood-sugar control in T2D	Mixed trials + contradictory meta-analyses	1–6 g/day	Mixed — real but inconsistent
Gum-disease treatment	No trials	—	Unproven
Cassia is safe at any chronic dose	Opposite — coumarin liver toxicity has a TDI	Chronic grams	Refuted

What dose was studied?

The oral finding used daily gum-chewing contact; blood-sugar trials ran 1–6 g/day. As a flavor-tier inclusion in an undosed dropper tail, cinnamon here is almost certainly sub-gram and sub-clinical: present for taste and label count.

Side effects

Contact stomatitis/oral lesions from cinnamon flavor (documented in dental literature), cassia coumarin liver toxicity at chronic high doses, and oil burns on undiluted mucosa.

Drug interactions

Blood-sugar drugs: additive lowering at gram doses.
Liver-toxic drugs: cassia coumarin adds liver load.

Who should not take it

Cinnamon-allergic individuals (the contact-lesion pattern is documented); liver-disease patients should avoid chronic cassia doses. At label levels the exposure is flavor-scale.

What the authorities say

The blood-sugar file is ‘inconclusive’ per systematic reviews; the coumarin TDI is a formal EU-style safety boundary; and the dental literature treats cinnamon sensitivity as a known cause of oral lesions: a richer file for harm-at-exposure than benefit-at-dose.

What to know about cinnamon

Cinnamon’s oral evidence depends on the preparation and mouth contact. An undisclosed amount cannot be compared with the chewing-gum study. Identify the species too: cassia and Ceylon differ in coumarin content, a relevant liver-safety consideration.

Frequently asked questions about Cinnamon

Does cinnamon help teeth or gums?

There's a real nugget: a human study found cinnamon-flavored chewing gum produced measurable reductions in salivary Streptococcus mutans, the cavity bacterium, consistent with cinnamaldehyde's laboratory antimicrobial action. It's a small single-study file and the delivery was sustained-chewing gum contact; whether trace cinnamon in a swallowed dropper does anything for plaque is unstudied.

Does cinnamon lower blood sugar?

The evidence is mixed. Early trials in type 2 diabetes reported fasting-glucose improvements at 1–6 g/day, but several later well-controlled trials and meta-analyses found little or no effect. It's the most-studied culinary spice for blood sugar and the answer remains 'maybe, small.'

Ceylon vs cassia — why does the species matter?

Cheap 'cinnamon' is usually cassia, which carries coumarin, a compound that is liver-toxic at chronic doses (the EU set a tolerable daily intake because of it). True Ceylon cinnamon has ~90% less coumarin. For a product taken daily and indefinitely, an unnamed species on the label is a real disclosure gap, not a technicality.

Is cinnamon safe?

Culinary amounts: yes, broadly. The cautions: cassia coumarin at chronic gram doses (liver), cinnamon-oil mucosal burns on undiluted contact, and contact stomatitis from cinnamon flavoring, a documented dental-clinic pattern. Cinnamon is a known cause of allergic mouth lesions in the dental literature.

Can cinnamon interact with medications?

Blood-sugar drugs get the main flag; additive glucose-lowering is plausible at gram doses. Coumarin (the compound, not the drug class; confusingly named) is processed by the liver, raising a theoretical warfarin-adjacent caution at high cassia intake.