You should make cinnamon tea with cinnamon barks, not with ground cinnamon. There are two types of cinnamon barks available on the market: Ceylon Cinnamon, also known as true cinnamon, and Cassia Cinnamon, the most common variety on the market. It is safer to use Ceylon Cinnamon sticks to make cinnamon tea since the coumarin content in Cassia Cinnamon is much higher. Coumarin is a substance that can cause liver damage if consumed excessively.