The seeds and young plants contain the alkaloid Protoanemonin. It can injure the digestive system and cause sores on the skin. The plants are the most poisonous when flowering and may cause death if eaten in large amounts.

Symptoms of poison are burning sensation of the mouth and skin, prickling sensation on the skin, nervousness, nausea, vomiting, low blood pressure, weak pulse, depression and convulsions.

The plants become harmless when dried. But if you are getting milk strait from the cow, watch out for milk with a bitter taste or a reddish color. The cows might have been eating Buttercups. This milk will make you very sick.