Warfarin was the first anticoagulant rodenticide, but today its use is declining as many rodents have grown resistant to it. Rodenticides are pesticides, often formulated into baits, that kill rodents like rats and mice.

Rodents include not only rats and mice, but also squirrels, woodchucks, chipmunks, porcupines, nutria, and beavers. As in humans, warfarin use stops normal blood clotting in rodents and leads to death, but may require several doses in rodents. Although rodents play important roles in nature, they can carry disease and may sometimes require control.

Some rodenticides are formulated without anticoagulant properties, including zinc phosphide, bromethalin, cholecalciferol, and strychnine. Many other rodenticides are formulated to stop normal blood clotting like the blood thinner warfarin, such as bromadiolone, chlorophacinone, difethialone, and brodifacoum.

More potent single-dose rodenticides are not sold to the public and are only allowed to be marketed to certified pest control professionals for application.

Warfarin was first registered for use as a rodenticide in 1950. Today, warfarin is primarily used in humans to prevent blood clots and help prevent stroke, heart attack or pulmonary embolism (blood clots in the lungs).

Is warfarin rat poison dangerous to other animals?

In addition to warfarin resistance, killing rats and other rodents with warfarin rodent poison led to another problem - the death of birds of prey like eagles, owls and hawks. These birds of prey hunt and eat the rodents that have ingested the poison.

Due to this, North American lawmakers moved to restrict the use of rodent poisons based on blood thinners, as studies show that the toxins accumulate in birds of prey and other animals. Today, the use of warfarin as a rodenticide is declining in the U.S.

In addition, rodent traps containing poison left outside can be consumed by other animals or pets -- and in the worst case scenario -- a child might get their hands on it.

• Rodenticides are usually formulated as bait to attract animals. They may contain added flavors like fish oil, molasses, peanut butter, ground meat, vegetables or fruit.
• Children and pets may find these attractive, and they should never be stored within their reach.

Always follow the instructions on the packaging when using any rodenticides, or seek the advice of a licensed pest management professional.

If any exposure occurs, contact the U.S. Poison Control Center at 1-800-222-1222 immediately and follow the first aid instructions from the Poison Control Specialist or the instructions on the product label.

This is not all the information you need to know about warfarin use as a rodenticide. Review the full product information and discuss this information and any questions you have with your doctor, other health care provider, or pest control professional.