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Pennyroyal oil toxic to pets

Q: Years ago, my mother used to put a drop of pennyroyal oil on each of our barn cats to control fleas. Now that I have my own cat, I planned to do the same, but I can’t find pennyroyal oil in the pet supply store. Do you know where I can get it?

A: Pennyroyal oil was once used to control fleas on pets, but no longer. We now know that, whether it’s applied to the skin or ingested, pennyroyal oil is toxic to cats and dogs.

The oil comes from two species of pennyroyal plants, which are in the mint family. When pennyroyal oil is applied to the pet’s skin, dermatitis can occur.

A more serious side effect is liver damage. Toxic signs, which may appear within two hours of exposure, include vomiting, lethargy and weakness. Without treatment, liver failure follows. It can cause nerve damage, seizures, hemorrhage, anemia and respiratory impairment. Pets have died after oral or even skin exposure.

Flea control has come a long way since your mother’s time. Products available through your veterinarian are tested for safety and effectiveness before they are marketed. Ask your vet to recommend a flea product for your cat. Some control fleas and ticks. Others prevent infection by fleas, heartworms, ear mites and two intestinal parasites, roundworms and hookworms.

If you buy a flea product from the pet supply store, make sure the label says it’s safe for cats, because some canine flea products contain chemicals toxic to cats.

Editor’s Note: What options are available for controlling pests in pets, and how do they work? Dr. Lee discusses tick and flea control options with a pet parent.

Lee Pickett, V.M.D. practices companion animal medicine. Contact her at

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