Cinnamon Side Effects: Dangers and Contraindications

Does cardamom/">cinnamon cause side effects? For occasional culinary use, very rarely. The point of caution mainly concerns Cassia cinnamon (Cinnamomum cassia, the type most commonly sold in supermarkets), which is rich in coumarin, a compound that can affect the liver with repeated, prolonged intake — unlike Ceylon cinnamon (Cinnamomum verum), which contains much less of it.

This article details what a pharmacovigilance study measured on this risk, and how to limit it in practice. For the Ayurvedic uses of nutmeg/">cinnamon, see our page cinnamon in Ayurveda; precautions already covered appear in cinnamon dangers.

What the coumarin study shows

The most solid reference on this risk is the study by Iwata, Kainuma, Kobayashi and colleagues, published in 2016 in Frontiers in Pharmacology. The researchers measured daily coumarin intake in 129 Japanese patients treated with a Cassia-cinnamon-bark-based preparation: on average, 0.113 mg of coumarin per kg of body weight per day, with 76% of patients exceeding the tolerable daily intake set by European authorities (0.1 mg/kg/day). Despite this frequent excess, the study found no significant difference in overall liver-test abnormalities between patients above and below the threshold (see the study on Google Scholar).

The important nuance the authors add: some people carry a genetic variant (a polymorphism of the CYP2A6 gene) that slows coumarin elimination, making them more exposed to a liver risk with regular, substantial consumption. There is no way to know beforehand whether you belong to this more sensitive group — hence the value of staying reasonable about quantities, especially with Cassia cinnamon.

Cassia or Ceylon: a difference that changes everything

	Cassia cinnamon	Ceylon cinnamon
Botanical name	Cinnamomum cassia	Cinnamomum verum
Availability	Most common (supermarket, bakery)	Rarer, often found in specialty stores
Coumarin content	High	Very low, near negligible
Regular concentrated use	To be limited (powder, capsules, cures)	Better suited to sustained daily use

For occasional culinary consumption (a pinch in a dish or a drink), the distinction hardly matters. It becomes relevant for regular, concentrated use — for example a capsule cure for blood sugar — see our article Kapha diet, where cinnamon holds a prominent place.

Other reported effects

• Mouth or digestive irritation: possible at a high dose of concentrated powder, linked to the bark's aromatic compounds.
• Allergic contact reaction: rare cases with cinnamon essential oil applied to the skin, never used undiluted.
• Effect on clotting: cinnamon has a theoretical mild anticoagulant effect, worth monitoring in combination with anticoagulant medication.
• Effect on blood sugar: a traditional and studied benefit, but one that becomes a point of caution with antidiabetic treatment (risk of a cumulative effect and hypoglycemia).

Who should be cautious with concentrated cinnamon?

• Known liver disease: favor Ceylon cinnamon, or seek medical advice before a concentrated Cassia cinnamon cure.
• Anticoagulant or antidiabetic treatment: medical advice before a regular concentrated-dose cure.
• Pregnancy: usual culinary use is not contraindicated, but concentrated cures should be avoided as a general precaution.
• Children: reserve for moderate culinary use, avoid concentrated supplements without medical advice.

Product quality, a factor not to overlook

As with any spice, a traceable origin limits contamination risk and lets you know precisely which cinnamon species you are consuming — a label simply reading "cinnamon" with no botanical detail often hints that it is Cassia. Our guide how to choose Ayurvedic supplements details the criteria to check before buying.

Cinnamon never replaces a prescribed treatment, particularly for diabetes or a liver condition. General safety guidelines for Ayurvedic herbs are detailed in our safety and precautions guide.