Cinnamon (Cinnamomum verum (Ceylon) and Cinnamomum cassia): Uses, Evidence and Safety

Cassia cinnamon contains coumarin, which can affect the liver. NCCIH (US) says interactions between coumarin and the liver have been reported, that some cassia products contain high levels, and that prolonged use could be an issue for sensitive people, such as those with liver disease. [1] And never swallow dry cinnamon powder as an internet "challenge": NCCIH calls it an unsafe dare where serious harm is possible. [1]

Which cinnamon?

Cinnamon is a spice from the dried bark of various Cinnamomum trees. [1] Two kinds matter here:

• Ceylon cinnamon, Cinnamomum verum J.Presl, called "true" cinnamon, grows mainly in Sri Lanka. [1][2]
• Cassia cinnamon, grown in southeastern Asia and the most common type sold in North America. [1] NCCIH names it Cinnamomum aromaticum (also known as Cinnamomum cassia). [1] This name is a trap: GBIF accepts Cinnamomum aromaticum Nees, while records named Cinnamomum cassia (L.) J.Presl are treated there as a synonym of a different taxon. [3] Labels may use either name, so read the species and plant part. See Ceylon vs Cassia Cinnamon and Botanical Names and Plant Parts on Labels.

NCCIH says products may not clearly say which species or part of the plant was used, and that species and parts differ in chemistry in ways that affect their impact on people. [1]

Traditional use

This is tradition, not proof. NCCIH says cinnamon's bark, leaves, flowers, fruits and roots have a long history of use in traditional medicine and cooking in many parts of the world, including China, India and Persia (Iran). [1] EMA (EU) has a herbal monograph for Ceylon cinnamon bark in the area of gastrointestinal disorders; we have not read its wording. [4]

What research shows

NCCIH (US, November 2024) says there have been many studies, especially for diabetes, but they are hard to interpret because it is often unclear which species or part was tested. It concludes that research does not clearly support cinnamon for any health condition. [1]

Results for a spice, a capsule, a nasal spray and cinnamon oil do not transfer to one another. For the oil, see Cinnamon Oil; for the tea, Cinnamon Tea.

Spice amounts versus supplement amounts

NCCIH says cinnamon is likely safe in the amounts commonly used in foods as a spice or flavoring. In larger amounts or over long periods it is sometimes linked to side effects, most often digestive problems or allergic reactions. [1] For the food side, see Cinnamon as a Food: Cassia vs Ceylon and Coumarin.

Safety

• Liver and coumarin: the German Federal Institute for Risk Assessment (BfR, 2010) describes coumarin as having liver-toxic and cancer-causing properties and says human data show a subgroup of people more susceptible to the liver effect than the animals studied. [6] It derived a tolerable daily intake of 0.1 mg per kg of body weight, confirming the earlier European Food Safety Authority value. [6] It also says dietary coumarin exposure comes mainly from cassia cinnamon, and that heavy consumers can reach an intake matching that limit. [6] NCCIH says Ceylon cinnamon may contain only a trace of coumarin. [1] Anyone with liver disease should ask a clinician. See Liver Safety and Supplements.
• Side effects: a systematic review of clinical trials, case reports and spontaneous reports found digestive upset and allergic reactions most common, mostly self-limiting; it cautioned that larger doses or longer use may cause significant effects and should be monitored. [7]
• Skin: cinnamon oil or powder on the skin may cause irritation or contact dermatitis. [1]
• Medicines: NCCIH says research suggests theoretical reasons that some components may interact with an anticancer medicine or nicotine. [1] Medicines for diabetes are not named in the NCCIH page; because supplements were studied for blood sugar, ask a pharmacist if you take diabetes medicine. See Supplements and Diabetes Medicines and How Interactions Work.
• Pregnancy and breastfeeding: some studies suggest Ceylon and cassia are safe in food amounts; NCCIH considers larger amounts of Ceylon cinnamon unsafe in pregnancy. [1] Little is known about larger amounts while breastfeeding. [1] LactMed found no data on cinnamon in nursing mothers or infants and no studies of milk supply. [8] See Pregnancy and Breastfeeding.
• Children, older adults, kidney, bleeding, surgery: not described in the sources we read. Tell the surgical team about any supplement.

Quality

Cassia cinnamon products can differ widely in coumarin. [1] LactMed warns that Ceylon cinnamon should not be confused with cassia, which contains high amounts of the toxic ingredient coumarin. [8] Look for the species and part on the label and see Quality Testing and Certifications.

We give no amounts for people. A clinician or pharmacist decides what suits a person.