Herb-Drug Interactions: Cinnamon

Cinnamomum cassia Blume and Cinnamomum verum J. Presl. and its varieties (Lauraceae)

Synonym(s) and related species

Cinnamomum cassia: Cassia, Chinese cinnamon, False cinnamon, Cassia lignea, Cinnamomum aromaticum Nees, Cinnamomum pseudomelastoma auct. non Liao.

Cinnamomum verum: Canela, Ceylon cinnamon, Cinnamomum burmannii (Nees & T. Nees) Bl. (known as Batavian cinnamon or Panang cinnamon), Cinnamomum loureiroi Nees, Cinnamomum zeylanicum Nees., Cinnamomum zeylanicum Blume.

Pharmacopoeias

Cassia Oil (British Ph 2009, European Ph 2008); Ceylon Cinnamon Bark Oil (British Ph 2009, European Ph 2008); Ceylon Cinnamon Leaf Oil (British Ph 2009, European Ph 2008); Cinnamon (British Ph 2009, European Ph 2008); Cinnamon Tincture (British Ph 2009, European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4).

Constituents

The bark of Cinnamomum cassia and Cinnamomum verum contains volatile oil mainly composed of trans-cinnamaldehyde, with cinnamylacetate, phenylpropylacetate,

salicylaldehyde and methyleugenol. Diterpenes including cinncassiols, and tannins such as cinnamtannins, are also present.

Use and indications

Both varieties of cinnamon are mainly used for digestive disorders such as diarrhoea, and flatulent colic or dyspepsia. Cinnamon has also been used for the common cold, and the oil may have antiseptic activity. It has been used in Chinese medicine for circulatory disorders.

Pharmacokinetics

No relevant pharmacokinetic data found.

Interactions overview

It has been suggested that cinnamon may interfere with the control of diabetes by conventional antidiabetic drugs, but controlled studies do not appear to support this suggestion. Cinnamon is a constituent of various Chinese herbal medicines, see under bupleurum9, for information.

Cinnamon + Antidiabetics

Although one study suggests that cinnamon may enhance the blood-glucose-lowering effects of conventional antidiabetics, a meta-analysis of controlled studies suggests otherwise.

Clinical evidence

In a placebo-controlled study, patients with type 2 diabetes were given Cinnamomum cassia 1 g, 3 g or 6 g daily (total of 30 patients) for a total of 40 days in addition to their normal medications. Blood-glucose levels were decreased by 2.9mmol/L, 2mmol/L and 3.8mmol/L in the 1 g, 3 g and 6 g groups, respectively. Changes in blood-glucose levels were only significant at 20 days in the 6g group (blood-glucose decreased by 2.8 mmol/L). No particular adverse effects were reported.

Experimental evidence

A literature review found several animal studies that suggested that cinnamon may have blood-glucose-lowering properties, but no direct interactions data were found.

Mechanism

Unknown.

Importance and management

Evidence is limited. The study cited above, which was not designed to investigate a potential drug interaction, seems to suggest that cinnamon has the potential to enhance the blood-glucose-lowering effects of conventional antidiabetic medication (unnamed). However, recent meta-analysis of randomised controlled studies, which included the study cited above, found that cinnamon does not appear to improve the control of type 1 or type 2 diabetes (glycosylated haemoglobin, fasting blood glucose and lipids assessed).

In general therefore, cinnamon would not be expected to markedly affect the control of diabetes with conventional antidiabetic drugs. If any effect does occur, it is likely to be picked up by standard blood-glucose monitoring, as high doses of cinnamon only had a significant effect on blood-glucose after 40 days of concurrent use.

Cinnamon + Carbamazepine

For mention that saiko-ka-ryukotsu-borei-to, of which cinnamon (Cinnamomum cassia) is one of 10 constituents, did not affect the pharmacokmetics of carbamazepine in an animal study, see Bupleurum + Carbamazepine.

Cinnamon + Food

No interactions found. Cinnamon is commonly used as a flavouring in foods.

Cinnamon + Herbal medicines

No interactions found.

Cinnamon + Ofloxacin

For mention that sairei-to, of which cinnamon (Cinnamomum cassia) is one of 12 constituents, did not affect the pharmacokmetics of ofloxacin, see Bupleurum + Ofloxacin.