Coltsfoot contains potentially liver-damaging pyrrolizidine alkaloids, with much higher levels appearing in the root than in the leaves or the flowers. Animal studies using amounts of coltsfoot hundreds of times higher than those used as medicine have shown these alkaloids can cause cancer in animals.⁷ A single case of an infant who developed liver disease and died after the mother drank tea containing coltsfoot during pregnancy has been reported.⁸ This eventually led to the banning of coltsfoot in Germany in 1992.

Coltsfoot should not be taken during pregnancy or breast-feeding.⁹ Otherwise, coltsfoot is generally safe.⁷

Coltsfoot should be differentiated from the plant called western coltsfoot (Petastites frigidus), because western coltsfoot can contain higher amounts of pyrrolizidine alkaloids. Use of western coltsfoot is not recommended.