Is Warfarin Really Rat Poison?

Q: I’m on warfarin. Is it true that I’m taking RAT POISON?

YES, you’re taking a medicine that originally was used to kill rats. We know warfarin, by the brand names Coumadin® and Jantoven® and as its generic name, warfarin. Warfarin is part of a group of plant-based compounds called coumarins. Coumarins are found in red clover and sweet clover as well as many other plants. In the early 1920s, some veterinarians noticed that at certain times of the year some cows had problems with bleeding. They called this phenomenon “sweet clover disease”  because it was eventually linked to cows that ate sweet clover hay which hadn’t been cured properly. Without proper drying, one of the compounds that naturally occurred in sweet clover was still active, and caused bleeding in the cows who ate the hay containing it. The compound responsible for the bleeding,  dicumerol, was identified in 1934 and by the early 1940s it was being tested in humans as a blood-thinning agent, or anticoagulant.

In 1945, a more potent cousin of dicumerol was patented by the Wisconsin Alumni Research Foundation (WARF) and named after it, called warfarin. Warfarin was first used as a rat poison or rodenticide because it was considered to be too potent to be safely used in humans, but after a blood test was developed to measure and adjust its blood-thinning effects, warfarin has become the most widely used oral anticoagulant in the United States.

By the late 1940s a close relative of warfarin called coumafuryl was marketed as a rodenticide or rat poison under the brand names Rat-A-Way® and Lurat®. Rats resistant to these early coumarins triggered the development of more potent, second generation anticoagulants called “superwarfarins”, such as brodifacoum, difenacoum, bromadiolone and difethiolone.  Brodifacoum is the rodenticide used by more than 50% of professional pest controllers in the United States.Today, 95% of rodent control in the United States is done with some form of anticoagulant.

I share my 18 years of experience helping people take their warfarin safely in my full-color handout How To Take Warfarin. It’s available as a FREE download here.

9 Responses to “Is Warfarin Really Rat Poison?”

  1. mdmiller says:

    I am sick of vomiting blood and going to the emergency room!!!! Warfarin will kill me if I don’t quit taking it NOW!!!!!!!!

  2. just a random thought says:

    If you are vomiting blood, stop taking it and go see a specialist immediately ! Just a tip !

  3. just a random thought says:

    This was a very good article ! I’ve always loved science, chemistry, medicine and medical procedures. What lead me here, was noticing a box of Eagle 7 rat poison. I always read the active chemical and % . I saw Warfarin was the main ingredient, with a different molecular structure. My mother-in-law takes warfarin and i never thought twice about it. Until today ! Nicotine was originally used as a pesticide as well. It is a transdermal poison that can cause rapid heart rates, increased BP, heart and liver failure in high concentrations. So, my thinking is as follows, why not add 7% nicotine to 0.025% warfarin for rat poison ? Arsenic is a good rodenticide. It causes the rats to run to a source of water as the body rapidly dehydrates. If you have no leaky pipes in your walls or under your house, the rat dies before they can get back inside the house.

    • Louise Achey says:

      Is your idea that the rapid heart rate and increased blood pressure will help the rat bleed to death more quickly from the warfarin-like compound in the rat poison?
      Arsenic is tasteless and odorless, so it would be hard for a rat to detect. Arsenic was widely used in pesticides in the United States from the 1890s to the 1960s and is still used in some insecticides, fungicides and as a rat poison. Small amounts of arsenic are also naturally present in soil and water.

  4. Quora says:

    Do you know if Warfarin is really used for rat poison, or if this is a long time rumor?

    Yes. Warfarin is used medicinally in humans as an anticoagulant and is also used as rat poison. http://askdrlouise.com/blog/is-warfarin-really-rat-poison/

  5. brenda says:

    I was wondering if Warfarin in still good for next year. We use at summer cottage when we close down for winter. Used to keep mice out of bunkie ( small cabin)

  6. I take warfarin for atrial fib. The skin is getting thicker on my legs. My finger nails are getting thin and splitting. Worse of all, my fingers are getting numb. I can hardly carry anything with my left hand because I can’t tell if I am holding it or not. My fingers feel gritty, or no feeling at all. I want OFF of the warfarin but must follow doctors orders. Is it the warfarin? I do not have diabetes or pre-diabetes.

    • Louise Achey says:

      PLEASE talk to your doctor about this! If you have noticed these symptoms after taking the warfarin then a short time off of it may help identify if it’s the culprit. Are you avoiding green vegetables? Many people are told to avoid them but I don’t. I believe green veggies are TOO IMPORTANT to good health to tell people to avoid them. I work with my patients on how to eat them regularly and they actually have more stable lab results than those who don’t eat green veggies. You can get more information about my system on how to eat greens while taking warfarin in my handouts on taking warfarin safely. They are available as a free download on my website http://www.askdrlouise.com.

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