Is Cinnamon Toxic to the Liver?

How do you know when an herb, spice or supplement is safe? It makes sense to do some reading on anything you are planning to take before you begin swallowing it. Many people are taking cinnamon to control blood sugar or lower cholesterol. However, there are several different varieties of cinnamon. Consequently, it is reasonable to ask: is cinnamon toxic if you take it as a supplement? Other plant products might cause trouble for the liver, including turmeric and quinine, found in tonic water.

Elevated Liver Enzymes Tracked to Tonic Water and Cinnamon:

Q. One summer my go-to beverage was diet tonic water. I’d drink it all day (no alcohol).

Towards the end of the summer, a routine blood test showed my liver values to be off the charts, although I felt fine.

While discussing this with my doctor, I remembered that years earlier a similar erratic blood test had prompted another doc to ask what had I eaten or drunk the night before my blood was drawn. When I answered, “gin and tonic,” she had said, “that’s okay then.”

This time around, I quit tonic water for life. After a month my liver values were going down. After three months they were still elevated, though. My doc asked me whether I had any other peculiar eating habits.

I did: I had gotten in the habit of chomping cinnamon sticks all day. He did some research, and I quit cinnamon. After another month, my liver was normal. Conclusion: apparently some people have a genetic pre-disposition to not be able to tolerate quinine. Cinnamon may also have an adverse effect on the liver for people like me.

Quinine and Cinnamon Can Tax the Liver:

A. Thanks for the reminder that even natural substances can have side effects. Quinine is known to cause dangerous blood disorders in some people. A study of adverse effects of this compound found that some sensitive individuals experienced liver toxicity after exposure to quinine-containing beverages such as tonic water (American Journal of Hematology, May 2016).

Cinnamon is a bit more complicated. Several animal studies showed that it can help protect against liver damage due to acetaminophen toxicity. At high doses, however, cinnamon may also harm the liver (Regulatory Toxicology and Pharmacology, June 2018). Keep reading to learn more about this interaction.

Cinnamon and the Liver:

Q. Is cinnamon toxic to the liver? I ended up in the emergency room after taking 1,200 mg of cinnamon daily for several weeks. I’ll never do that again.

Know Your Cinnamon:

A. Cassia cinnamon, the type you normally find on the spice shelf in the supermarket, contains variable levels of coumarin (Journal of Agricultural and Food Chemistry, Oct. 13, 2010). This compound can harm the liver (Molecular Nutrition & Food Research, Feb. 2010).

To Avoid Toxicity, Stick with Water-Based Extracts:

Anyone who wants to use cinnamon to lower cholesterol or blood sugar would be well advised to stick with an aqueous extract because coumarin is not water-soluble. A person could purchase this in capsule form and avoid coumarin.

Is Ceylon Cinnamon Toxic?

Another option would be to use Ceylon cinnamon (Cinnamomum zeylonicum, true cinnamon or Cinnamomum verum). This is a different species that does not contain significant amounts of coumarin. It is more expensive, however.

There is some preliminary evidence that it too can help lower blood sugar and cholesterol (Journal of the Academy of Nutrition and Dietetics, Nov. 2016). An earlier review suggested that Ceylon cinnamon has antimicrobial activity and can lower blood sugar, cholesterol and blood pressure; it may be useful against stomach ulcers and seems to help protect the liver (BMC Complementary and Alternative Medicine, Oct. 22, 2017). There are too few clinical trials to be certain of these benefits, however.

In another study, researchers found high levels of E-cinnamaldehyde, an anti-inflammatory compound, in both C. zeylanicum and C. cassia (Food & Function, March 2015).

What Should You Do?

People who include spices or dietary supplements in their regimen should monitor their progress with regular blood sugar tests. If you don’t know whether the cinnamon you are using is really Ceylon cinnamon, you should stick with the water extract or ask the doctor to monitor your liver enzymes regularly. In addition, it is not a good idea to combine cinnamon or any other supplement with medications unless a physician has investigated and approved the combination.

Was the dose too high? The research on cinnamon has used doses as high as 6 grams (6,000 mg). The 1,200 mg you were taking is in the same range as a dose being tested in a study currently being conducted, the CINNAMON trial (Cinnamon Trial-lIfestyle iNtervention Plus Water-soluble CiNnAMon Extract On loweriNg Blood Glucose in Pre-diabetics). We expect the results of this study should provide some answers about the safety and efficacy of cinnamon for lowering blood sugar.

Herbs and Liver Injury:

As far as we can tell, drugs are far more likely to cause harm to the liver than herbs such as cinnamon, quinine or even turmeric. A report last year made some headlines as it implicate the popular yellow spice turmeric in a handful of cases of liver damage (American Journal of Medicine, Feb. 2023). In their report on ten cases, the researchers suggested that current products designed to optimize absorption might increase exposure to the plant compounds. Moreover, they found that 70% of the cases had a specific genetic makeup that could increase their vulnerability.  Their bottom line? Do not assume that more is better when it comes to plant phenols.