Alternate names

Water hemlock, poison parsnip, poison parsley

Toxicity to pets

Cowbane, which is more commonly known as water hemlock, poison parsnip, or poison parsley, is often referred to as the most violently toxic plant in the United States. Cowbane is considered a natural wildflower and prefers wet areas, such as irrigation ditches, marshes, damp areas in pastures, and riverbanks. Cowbane contains the toxins cicutoxin and cicutol, which affect the neurons in the brain and central nervous system. All parts of the plant are poisonous, with the roots containing the highest concentration of the toxin. It is highly poisonous to horses, and only takes about 0.2 to 2 lbs hemlock root per 1,000 lbs of a horse’s body weight to cause death. Clinical signs include drooling, dilated pupils, weakness, agitation, nervousness, twitching, seizures, cardiac abnormalities, difficult breathing, and death from respiratory paralysis.

Content written by: Dr. Lynn Hovda, DVM, RPH, MS, DACVIM, Pet Poison Helpline®


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The content of this page is not veterinary advice. A number of factors (amount of substance ingested, size of the animal, allergies, etc.) determine what is toxic to a particular pet. If you think your pet has eaten something potentially toxic, call Pet Poison Helpline or seek immediate veterinary treatment.