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Grey cat staring at a rat

Mouse poisons can kill pets and wildlife

Q: I need to put some mouse poison in the basement, but I'm worried my cats may find it. I understand that poisoned mice bleed to death. Can mouse poison have the same effect on cats?

A: Yes, and worse.

The first rodenticides were anticoagulants, which caused death from internal bleeding. Short-acting chemicals like warfarin became less effective as rodents developed resistance, so companies developed longer-acting, more toxic anticoagulants such as brodifacoum, bromadiolone, difenacoum and difethialone.

These products are still available, but their use has been somewhat restricted, and even more effective—that is, toxic—rodenticides have been developed: bromethalin, cholecalciferol and zinc phosphide.

  • Bromethalin targets the central nervous system, causing tremors, loss of coordination, seizures, paralysis and death. Cats are 10 times more sensitive to bromethalin than dogs.
  • Cholecalciferol is actually vitamin D3, which increases calcium levels in the blood and therefore affects all body systems. High levels cause heart problems, kidney failure and death.
  • Zinc phosphide is converted in the body to highly toxic phosphine gas, which smells like rotten garlic or dead fish. If your cat is exposed, rush to the veterinary hospital with the car windows open, because if you can smell the gas, you are already being exposed to potentially toxic levels. Fortunately, zinc phosphide is the least popular of these rodenticides.

Anticoagulants, bromethalin, cholecalciferol and zinc phosphide kill rodents as well as cats, dogs, raptors, other wildlife and humans. Nontarget species are exposed by eating the bait or through relay toxicosis, which occurs when mice that ingested the toxin are eaten by predators such as cats.

It would be safer to use other forms of mouse control in your home. Cut off the rodents' food supply by, for example, storing bird seed and pet food in tightly closed metal containers. Plug gaps in your foundation so mice can't enter.

Place humane traps in the basement, and release the captured mice outdoors. Consider snap traps or electronic traps, or invite your cats to take on the job of rodent control.

Editor’s Note: If you suspect that your pet has ingested a toxic substance, do not wait for symptoms to appear. Call your veterinarian or the Pet Poison Helpline at (855) 764-7661 immediately. Do not induce vomiting unless you are instructed to do so; many toxic substances are corrosive and can cause more damage.

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

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