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One note of caution is that coumarin, a substance found in cinnamon, may trigger cancer in animals. Cinnamon also contains cinnamaldehyde, which is toxic. But these toxic components are fat-soluble, while the beneficial ingredient, proanthocyanidin, is water-soluble. Water-soluble extracts of cinnamon are available in which “all the bad components are left behind,” said Anderson. (Ground cinnamon does allow both water- and fat-soluble components to be absorbed, but at the doses recommended, it does far more good than harm, he said; cinnamon sticks placed in hot water release only water-soluble components.)

Found here.

If you google with key words "cinnamon" "MHCP" and "coumarin", you will see many more articles with similar information. The moral of the "story" is you CAN get too much of a good thing. Personally, I think putting cinnamon in tea or coffee to get just the water-based extract is the best idea.