How Does Rat Poison Work?

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Rat poison is an unpleasant tool to have to use, but when faced with a fast-growing rat colony, we often don’t have much of a choice. What is in rat poison, however, and what happens to rats when they eat poison? People love to compare various strong alcohols and liquids to rat poison to the point where the phrase has turned into a byword of sorts but how does a rat poison work exactly?

The fact of the matter is that there are all sorts of chemicals that can be used and have been used as rat poison. Rats are lively and sturdy animals with a lot of built-in resistances but at the end of the day, they are just mammals like any other. Still, as of today, there are several types of rat poison that are much more popular than others thanks to their fast-active effects, ease of use, and relative safety for you, your family and pets, and the environment. Emphasis on “relative”.

Anticoagulant rat poison

If you want to know how to kill rats, then anticoagulants are by far the most popular type of domestic rat poison today. They work on the same simple principle that human blood thinning medicine does – they prevent blood clotting. Only, of course, rat poison contains a much higher dose of anti-coagulants that aim to outright kill the animal.

These anticoagulants work by depleting the Vitamin K stores in the rodent’s system and preventing its future production in the intestinal tract. Once this is done, it’s only a matter of a couple of days until the rodent loses its entire supply of Vitamin K. The most common type of anticoagulant used to be warfarin, however, in recent years rats seem to have developed a resistance to it, so stronger and much more powerful anti-coagulants have been developed such as Bromadiolone (also known as “super-warfarin”).

Additionally, anticoagulant rat poison also includes anti-coagulants such as 4-hydroxycoumarin and indandione. The task of these chemicals is to cause trauma to the blood vessel walls of the rodents which increases the risk of internal bleeding. Once the rodents start bleeding internally and they are depleted of Vitamin K, the bleeding can’t stop because the blood can’t clot and the pests die from internal hemorrhaging.

As for how long does it take for rat poison to work, in the case of anti-coagulants it usually takes a couple of days for the rats to start dropping.

The reason why this is such a popular type of rat poison nowadays is that rat poisoning is treatable if humans or pets are subjected to it. Taking additional Vitamin K is the obvious immediate solution to poisoning from anti-coagulant rat poison, although we can’t stress enough how important it is to immediately go see a doctor regardless of whether you’ve taken Vitamin K or not.

Phosphide rat poison

Another type of rat poison that’s fairly popular nowadays is phosphides rat poison. It’s typically made out of zinc phosphide and it works by reacting to the rodent’s stomach acid and forming a gas called phosphine which kills the vermin rather quickly. The reason why phosphides can be a good choice, particularly for homeowners with pets, is that the dead rats are not poisonous themselves. Where with anti-coagulant rat poison, eating a poisoned rat can in turn poison your cat or dog, with phosphide rat poison that’s not the case.

On the flip side, consuming phosphide rat poison directly from the container will cause immediate vomiting and there isn’t an antidote to it as there is to anti-coagulant rat poison. In other words – use it with a lot of care as the rat poison effects from phosphide are severe.


Calciferols are another relatively common type of rat poison and they work by affecting the level of Vitamin D in the rodent’s body. Where anti-coagulants worked by reducing Vitamin K, however, Calciferols work by increasing the level of Vitamin D. Why this may sound nice at first, higher levels of Vitamin D actually cause hypercalcemia or an increased amount of calcium in the body. This, in turn, leads to damage to the stomach, heart, kidneys, blood vessels, lungs, and other vital organs due to calcification. It’s a nasty but effective way to kill rodents as they usually die within a day of consuming the poison. In fact, a lot of rat poison products use a combination of Calciferols and anti-coagulants.


This chemical has fallen from favor as a rodenticide due to its dangerous side effects to humans, pets and the environment. It is, however, infamous and can still be used by professionals for below-ground poisoning. Strychnine is a very toxic, colorless and bitter crystalline alkaloid. It can cause poisoning, convulsions, and death from asphyxia not just through ingestion but even just from inhaling it or from absorbing it through your skin, eyes or mouth.

There are lots of other types of rat poison, of course. After all, there are a lot of ways to kill a mammal. These are the most popular types, however, particularly in commercial rat poison. You can try and make a homemade rat poison if you want – people attempt various mixtures:

  • Plaster of Paris, cornmeal, and milk;
  • Flour, sugar, baking soda;
  • Plaster of Paris and instant potatoes.

There are also other recipes as well, some of them can be effective to a certain degree but few are as potent as commercial rat poisons.

Speaking of effectiveness, keep in mind that even a powerful commercial rat poison is unlikely to deal with an entire rat infestation by itself and will typically do about 50% of the work. That’s why rat poisons are best used in combination with rat control methods such as electric rat traps . Also keep in mind that rat poisons are not only toxic and dangerous to your pets and kids, but they also leave your home with a bunch of dead rats, usually hidden in inaccessible places such as inside the walls, inside hollow ceilings, etc. So, in short – use rat poison with care and with plenty of forethought.

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