Ceylon cinnamon, which is native to Sri Lanka, is more difficult to find and more expensive. Its scientific name is Cinnamomum zeylanicum, and it is also known as Cinnamomum verum -- "verum" means "true."
A 2012 review article published in "Diabetic Medicine" examined 16 studies of Ceylon cinnamon specifically. The researchers uncovered beneficial effects on diabetic complications, with no toxicity to the liver and kidneys. Toxicity might, however, be an issue for cassia.
Ceylon cinnamon has a sweeter, more delicate flavor than cassia cinnamon does, which may make it preferable for flavoring desserts and lighter dishes. But the more important distinction may be the presence of a chemical called coumarin, a natural plant chemical that acts as a blood thinner. This chemical is present in much higher concentrations in cassia than in Ceylon cinnamon. It is contraindicated for anyone taking prescription blood thinners. Coumarin has also been shown to be toxic to the liver and kidneys, and it may also be carcinogenic, which can negate any health benefits of cinnamon.
In addition to its potential beneficial effect on glucose metabolism and body weight, Ceylon cinnamon also contains antioxidant compounds called proanthocyanadins. These are similar to the antioxidant compounds found in green tea and grapes. Coumarin-free Ceylon cinnamon may also be beneficial to the liver, according to studies reviewed by "BMC Complementary and Alternative Medicine" in 2013, with no adverse effects to other organ systems. Other benefits may be antimicrobial and anti-parasitic activity, digestive health and blood pressure reduction.