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How Long Does It Take For Rat Poison To Work?

Rowan Burgess |

In October 2019, pest control chiefs warned that the UK's population of 120 million rats (nearly double the human population of 67 million) would soon be scurrying into homes to escape the winter cold. 

Since time immemorial, rats have been a constant thorn for humans. They pollute food and water and are super-spreaders for several ailments such as the bubonic plague and typhus. Rodents also cause structural damage to homes and buildings.

If you are battling a significant rat infestation, rat poison is the fastest way to reduce your home or building population. But if you've set the baits, you may be wondering, "How long does it take for the rat poison to work?" 

Let's explore that topic.


Factors That Affect the Effectiveness of Rat Poison

Before we answer how long it takes for the poison to kill rats, let's discuss the factors that affect its effectiveness. 

#1. Is It First-Generation or Second-Generation Rat Poison? 

When looking to purchase rat poison, you'll likely come across two categories of rodenticides. 

The first-generation poison will kill rats slowly, and it needs to feed on the toxin multiple times. Some examples of first-gen toxins are Warfarin and Diphacinone. 

Second-generation poisons are fast-acting, and the rodent only needs to feed on it once for its lethal effects. Brodifacoum is a popular second-gen poison. 

When using such poisons, rodents can develop bait shyness if you don't remove dead rats from the vicinity quickly. The rodent starts to associate the dead rodents with the bait. 

This awareness is unlikely to happen with first-gen poisons as the rodents need multiple feedings before dying. 

#2. Have the Rats Developed Resistance to These Chemicals? 

Some of the first-generation poisons have been around for decades. For example, Warfarin's use as a commercial rat poison in 1948 was a significant development in combating rat infestation in the United States. However, over time, some species have developed resistance to the effects of Warfarin. 

#3. Does the Rodent Have Other Sources of Food Asides from the Rat Bait? 

If there are other food sources for rodents in the infested home or building, they will likely avoid the bait station. Rats are habitual feeders, so they are likely to avoid a new feeding point if they can still access their previous feeding points.  

Before you set out rat poison, ensure you clear out or make other food sources inaccessible. It's a good rule of thumb to get toxins that smell similar to the food they eat. 

#4. Have You Placed the Poisons Correctly? 

When placing a rat bait, you must set it correctly. The placement ensures that your pets don't eat the bait and that bad weather conditions don't disrupt or dilute it from working. 

One way to ensure rat baits' effectiveness is to use a bait station or a snap trap. These stations have two benefits. 

First, it protects your pets and children from coming in contact with the toxin. 

Second, it offers you the opportunity to recreate an environment that the rodent is familiar with whenever it comes to feed. Rodents love familiarity, so they are usually suspicious of anything that looks out of place. 

How Long Does It Take for Rat Poison to Work?

The timeline depends on what generation of toxins you purchase for rat control

If you buy a first-generation rodent poison, it will usually take about seven days for the rodent to die. The reason is that the lethal dose takes multiple feeding sessions. 

A second-generation poison can kill the rodent from internal bleeding in two to three days. It has a faster efficacy rate.

One significant advantage of second-gen poisons is secondary poisoning is unlikely to occur due to their high toxicity. Secondary poisoning is when an animal further up the food chain eats the poisoned rodent and dies due to ingesting the poison. If your dog eats the rat by accident, you won't have to worry about it affecting your beloved pet.

Besides the generation type, however, the time it takes for the rat poison to act can also depend on the various factors mentioned above that might limit the efficacy.

What You Can Do to Increase the Effectiveness of Rat Poison

Rodents are not only picky eaters but also they can be quite intelligent. They learn quickly, meaning the smarter ones will start "bait avoidance" once they notice a problem with their food or usual feeding paths. 

Here are some ways to counter these sly creatures and increase the effectiveness of rat poison. 

#1. Ensure You Use Fresh Rodenticides 

Whenever you have a rat problem, ensure you use fresh rodenticides. You don't want to use a pack you've had stored in your basement or since the last infestation. 

You need a fresh set because you have a higher probability that it might have expired. It's also possible that various factors, such as the storage conditions, might have reduced its effectiveness. 

Using expired rodenticide in such cases will help the rodent develop resistance to that particular toxin.

#2. Constant Clean-Up of The Bait Area

Once you set up the rat trap, you need to inspect the area frequently. Replace any bait that the rats have eaten with fresh bait and remove any leftovers.  

Also, check the surrounding area for any dead rats. These steps will reduce the chances of bait shyness occurring. 

#3. Use Pre-Bait to Encourage the Rodents to Eat the Poison

Rodents will usually nibble at the food and move onto the next meal to avoid poisoning. If the rat doesn't fall sick after a day, it will come back for another bite. 

If it does fall sick, the rat will avoid any meal with that same taste, smell, or flavour. 

To prevent this from happening, you can use pre-bait with the same flavour, taste, and smell as the toxic bait some days before placing the poisonous bait. That way, the rodent associates smell and taste with positive outcomes and will not avoid it when you switch it to a toxic option after a couple of days. 

#4. Remove Alternate Food Sources 

Before setting out bait, use tightly sealed containers they can't gnaw through to get food. By doing this, the rodent will have no other choice but to eat or at least taste the bait. 

You should also use metal containers that are harder to open for storing your garbage. 

#5. Place the Rat Poison in the Appropriate Areas

Where you put the poison is vital to its effectiveness. Look out for any areas where you have high concentrations of rodents' faeces and urine. Those areas are where you need to place your baits. 

Once you place the baits, ensure you don't move them around. 

Rats notice when an object has moved around and might avoid it. If the rodents haven't touched the bait for a while, you'll need to move it. 

Finally, ensure you place the baits between the food supply and where you think might be their habitat. Usually, you want to look for densely covered areas. Rodents love to rest and feed in these sorts of places. 

Frequently Asked Questions

Why Are Rats Eating Bait but Not Dying?

There can be several reasons why rats are eating bait but not dying. Firstly, anticoagulant-based poisons have delayed effects, allowing rats to consume some without immediate death. Secondly, if alternative food sources are available, rats may not consume enough bait to reach a lethal dose. Lastly, rats may have developed resistance to the specific poison being used, reducing its effectiveness.


By now, you have a clear idea of how long it takes for rat poison to work. If you still aren't sure if you should use a second-generation or first-generation poison, you can ask yourself the following questions: 

  • Do you have pets that are at risk of secondary poisoning? 
  • Do you have wildlife around your home that might ingest the poison after eating the rodents' dead carcass and die of internal bleeding?

No matter which type you end up buying, make sure you keep it out of children's and pets' reach.