Coumarin

Phytochemical

What is it

Coumarin is a naturally occurring aromatic compound (a benzopyrone) found in many plants, including tonka beans, sweet woodruff, cassia cinnamon, and sweet clover. It has a sweet, hay-like vanilla scent and is used widely in perfumery, but its use as a food additive is restricted in many countries due to liver toxicity concerns.

Evidence for 2 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Fragrance and flavoring

Strong Evidence

Coumarin is widely used in perfumery (not a health benefit). Food use is regulated or banned in many jurisdictions.

Lymphedema (high-dose historical use)

Mixed Evidence

Coumarin was studied at 100 to 400 mg/day for high-protein edema and lymphedema, but trials were halted or restricted due to hepatotoxicity. Modern guidelines do not recommend coumarin for these uses.

How it works

Coumarin itself is not pharmacologically equivalent to the anticoagulant drug warfarin, despite the related name. Warfarin and other anticoagulants are derivatives produced by the oxidation of coumarin to 4-hydroxycoumarin and subsequent fungal modification in spoiled sweet clover hay. Pure coumarin does not significantly inhibit blood clotting. Ingested coumarin is rapidly absorbed and almost entirely metabolized in the liver, primarily by CYP2A6 to 7-hydroxycoumarin, which is conjugated and excreted in urine. In a small fraction of people (particularly those with CYP2A6 variants), an alternative pathway produces o-hydroxyphenylacetaldehyde, a hepatotoxic metabolite that can cause liver injury at chronic doses above approximately 0.1 mg per kg body weight per day. In cancer and lymphedema research, high-dose coumarin (often 100 to 400 mg/day) was historically studied as an immune modulator and lymph drainage agent, but trials ended due to hepatotoxicity in a small but meaningful fraction of patients.

Dosage

There is no recommended intake. The European Food Safety Authority sets a tolerable daily intake of 0.1 mg per kg of body weight per day (about 7 mg/day for a 70-kg adult). Cassia cinnamon can contain 2 to 8 mg coumarin per teaspoon, making it easy for heavy cinnamon users to exceed this limit. DSLD data for coumarin as a standalone supplement are very limited.

When and how to take it

There is no recommended timing for coumarin supplementation, which is not advised due to liver concerns. Dietary exposure through cinnamon is generally divided across meals, which does not change cumulative liver exposure.

2 commercial forms

Compare the main delivery options and what they’re best suited for.

Synthetic coumarin

Used as a fragrance ingredient. Not approved as a food additive in the U.S.

Identical chemically to plant-derived coumarin.

Cassia cinnamon (dietary)

Most ground 'cinnamon' sold in the U.S. is cassia and contains substantial coumarin. Ceylon cinnamon contains far less.

Coumarin content varies between 2-8 mg per teaspoon depending on origin.

Safety

Chronic intake above 0.1 mg/kg/day risks liver injury (transaminase elevation, hepatitis) in susceptible individuals. The U.S. FDA banned coumarin as a food additive in 1954 because of toxicity in animals. Acute toxicity is low. Allergic skin reactions can occur from topical exposure in cosmetics.

Who should be cautious

Avoid supplemental coumarin in pregnancy, breastfeeding, and in people with any liver disease. Heavy users of cassia cinnamon should be aware of cumulative coumarin exposure; Ceylon (true) cinnamon contains far less coumarin and is a safer choice for daily use.

Interactions

Coumarin itself is not an anticoagulant, but it should not be confused with warfarin. Co-administration with hepatotoxic drugs or alcohol may compound liver risk. CYP2A6 inducers or inhibitors could alter coumarin metabolism and toxicity.

Food sources

Cassia cinnamon

Amount
1 tsp (~2.6 g)
%DV
—

Tonka bean

Amount
1 bean
%DV
—

Sweet woodruff

Amount
1 g dried
%DV
—

Frequently asked questions

Is coumarin the same as warfarin?⌄

No. Warfarin is a synthetic anticoagulant derivative of 4-hydroxycoumarin. Plain coumarin does not have meaningful anticoagulant activity.

Why is coumarin banned as a food additive?⌄

Studies in animals and case reports in humans demonstrated liver toxicity at chronic exposure levels achievable through food. The U.S. FDA prohibited it as a direct additive in 1954.

Should I worry about coumarin in cinnamon?⌄

Heavy daily cassia cinnamon use can exceed the European tolerable daily intake. Switching to Ceylon cinnamon eliminates most of the risk.

Does coumarin have any health benefit?⌄

No well-supported health benefit at safe doses has been established. The lymphedema studies that used higher doses ended due to liver toxicity.

References

Coumarin on Wikidata — Wikidata link

Coumarin (ChEBI:28794) — ChEBI link

Coumarin (PubChem CID 323) — PubChem link

Coumarin on NIH DSLD (US supplement label database) — NIH Dietary Supplement Label Database link

Research on Coumarin (PubMed search) — PubMed link

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Evidence-based·How we grade evidence

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you’re pregnant, breastfeeding, on medications, or managing a chronic condition.