This spice is famous throughout the world due to Cinnamon rolls and Danish Pastries. Cinnamon is a rolled bark which contains aromatic oils. The bark curls and usually have dark maroon brown to light mustard brown color. Originated from South Asia, there are two types of cinnamon. Cassia variety which is cheap and available in abundance, have rich flavor and aroma and usually used in cuisine. It is cultivated in Indonesia, Vietnam and China. Then there is true cinnamon aka Cinnamon Verum. It is the medicinal cinnamon that is prized and so it has high price. Cultivated in Sri Lanka, thus commonly known as Ceylon Cinnamon. It is also cultivated in some parts of southern India.
Cinnamon have something called coumarin, not to be mistaken with Turmeric curcumin which is beneficial. This coumarin is toxic to liver and kidneys even in small quantity. Whereas Cinnamon also contain cinnamaldehyde which imparts the medicinal benefits. The benefits are observed in Diabetic patients, who consumed True cinnamon daily for short period and noticed reduced fasting glucose levels. Though the research is still underway but unless they can find way to patent or commercialize it as drug, it wont be profitable.
Now the thing is, whether you should consume cinnamon or not? Well, I too was researching on cinnamon primarily because of its hypoglycemic effects on diabetes. I read journals and bought cinnamon from stores only to find them to be cassia. In markets and online, most brands are selling cassia by labeling it Ceylon cinnamon. I tried several and all of them failed. They tasted good and rich aroma but not too good for health.
I am still in search of true cinnamon with consistent quality, but most manufactures just blend it with cassia or switch to cassia once their sale increases. Therefore, I suggest you purchase the cinnamon sticks that looks like these in picture below. And grind them in home either manually or using a spice/coffee grinder. And when it comes to spice, always buy premium. Even though it may be expensive, but the quality and effects are worth it. To consume cinnamon, you can add teaspoon full in smoothies, porridge, baked goods or beverage. I add in coffee or tea. Prefer to take it in warm beverage or food to boost its effect. There are some cinnamon that does not dissolve in liquids and have grainy taste.