Many of us have added liberal doses of cinnamon to our diets because it helps control blood sugar.
However, in such cases, we need to be careful only to use Ceylon (or true) cinnamon. Other types can damage the kidneys and liver.
I’ve done some checking and it appears that the following from Wikipedia is correct:
Due to the presence of a moderately toxic component called coumarin, European health agencies have recently warned against consuming large amounts of cassia. This is contained in much lower dosages in Cinnamomum burmannii due to its
low essential oil content.
Coumarin is known to cause liver and kidney damage in high concentrations.
True Ceylon cinnamon has negligible amounts of coumarin.