The seeds and young plants of the larkspur are toxic to both people and animals. Toxicity decreases as the plant ages. Larkspur has several alkaloids including delphinine, delphineidine, ajacine and others that can cause very unpleasant issues. According to the USDA, symptoms of poisoning include general weakness and muscle spasms, as well as abdominal pain and nausea. Eventually, it can lead to respiratory distress, paralysis and death.
Larkspur is responsible for heavy livestock losses, particularly with cattle in western states when the animals are allowed to graze where the plant is abundant.