Little doses of cinnamon are probably OK for most people, but there may be risks if you eat a lot of it or take supplements containing cinnamon.
Because of its high coumarin content, cinnamon stick is a major cause for alarm. Naturally occurring coumarin may be found in various plants, including cinnamon, and it has been linked to liver damage when consumed in excess. The most popular cinnamon form, cassia cinnamon, has more coumarin compound than the milder and sweeter Ceylon cinnamon.
In addition, several drugs, such as blood-thinning medications, may interfere with excessive cinnamon consumption or cinnamon supplements. Due to the presence of chemicals in cinnamon that might have blood-thinning effects, it should be avoided by those on anticoagulants since it may increase the risk of bleeding.
Cinnamon sticks, in moderate quantities, is safe for pregnant women and children. Supplemental cinnamon is not suggested for pregnant women since its safety has not been proved.