Mainly there are two type of varieties of cinnamon named as Cinnamon and Cassia. Therefore Cinnamon and Cassia are like cousins and these are the two oldest species known to mankind. Out of these two types, Cinnamonum verum is considered as the true cinnamon while, Cinnamon cassia is a low quality cinnamon.
Coumarin is known to cause liver and kidney damage in high concentrations. True Ceylon cinnamon has negligible amounts of coumarin. Ceylon Cinnamon has between 2-5 ppm of coumarin compared to Cassia (2000-5000 ppm). Ceylon Cinnamon has between 0.001-0.005 milligram of Coumarin per tea spoon. Cassia has atleast 1000 times more Coumarin than Ceylon Cinnamon. All other varieties of Cinnamon, except Ceylon Cinnamon, have much higher coumarin content.