Yes, coumarin is used in rat poison, and cassia bark contains coumarin, but rodent metabolism is very different from humans. A healthy human would have to eat 275mg per kilogram of body weight (2 1/2 tsp. of cinnamon) to have a 50% chance of consuming a lethal dose. For a 110-lb woman, that’s over half a pound of cinnamon.

Coumarin can be problematic for people who have compromised liver function, or have a rare sensitivity to it. Cassia “cinnamon” contains 4-5% coumarin by weight.

The 1/2 teaspoon in this recipe (1.15g) would contain about 57 mg total, and each serving (the recipe serves about six) would contain less than 10mg. The recommendation for people who might be sensitive to coumarin is 1mg/kg of body weight. A 120-lb. individual with compromised liver function would have to eat the whole pot to exceed the recommended limit.

Lots of foods have toxic compounds – almonds, stone fruit seeds, and apple seeds contain cyanide compounds. Rutabaga, spinach, and beets contain oxalic acid. Plants don’t want to be eaten. However, for the average healthy person, these compounds present little to no risk, and it irks me that panic-mongers want to make food “dangerous.” No wonder the American diet is so damned pitiful.

Cassia has a chemical called coumarin which could be toxic. Please click the below link to read more.

http://www.bfr.bund.de/cd/8487