Bromadiolone is a powerful rat poison classified as a second-generation anticoagulant rodenticide, sometimes called a “super-warfarin.” It was patented in 1967 and is used worldwide to kill rats, mice, and voles, including rodent populations that developed resistance to older poisons. It works by preventing blood from clotting, causing fatal internal bleeding in animals that consume it. Because it’s far more potent and longer-lasting than earlier rodenticides, it poses serious risks to pets, wildlife, and humans who encounter it accidentally.
How Bromadiolone Kills Rodents
Your body constantly recycles vitamin K, a nutrient essential for making the proteins that allow blood to clot. Bromadiolone blocks the enzyme responsible for that recycling process. Without functional vitamin K, the liver can’t produce working versions of four critical clotting factors. The result is that even minor internal injuries can’t heal, and the animal slowly bleeds to death internally.
This mechanism is the same one used by the blood-thinning drug warfarin, but bromadiolone is dramatically more potent. As a second-generation compound, it was specifically designed to overcome the genetic resistance some rodent populations had developed against warfarin and other first-generation poisons. It also accumulates in the liver, meaning a single feeding can deliver a lethal dose rather than requiring multiple exposures over several days.
The lethal dose for rats is roughly 1.6 mg per kilogram of body weight. Death doesn’t happen immediately. Rodents typically die days after consuming the bait, which is why they don’t learn to associate the bait with danger.
What Bromadiolone Bait Looks Like
Bromadiolone in its pure chemical form is a white to yellow powder, but commercial bait products are dyed red or pink so they can be distinguished from food. The poison is typically mixed with grains like rice or corn at a concentration of 0.005% by weight. It comes in several forms: solid blocks, paste, pellets, and liquid formulations that are mixed with grain. The resemblance to food is intentional (to attract rodents) but creates a real hazard. Cases of accidental human poisoning have occurred when people mistook pink-dyed grain bait for food products like red yeast rice.
Signs of Poisoning in Humans and Pets
Because bromadiolone disrupts clotting rather than acting as a traditional poison, symptoms can take days to appear. The earliest signs are often subtle: unusual bruising, bleeding gums, or nosebleeds. As the poisoning progresses, more serious symptoms develop, including blood in urine or stool, vomiting blood, pale skin, and low blood pressure. In severe cases, bleeding can occur in the brain, causing confusion or altered consciousness. Death can happen as late as two weeks after exposure.
Dogs are the most commonly poisoned pets because they’ll eat bait blocks or consume poisoned rodents. The same bleeding symptoms apply. If you find evidence that a pet has gotten into rodent bait, the delay before symptoms appear is not a reason to wait. Treatment is far more effective when started early.
Treatment Takes Months, Not Days
The antidote for bromadiolone poisoning is vitamin K1, which bypasses the blocked recycling enzyme and restores the body’s ability to produce clotting factors. In acute cases, patients may also receive transfusions of plasma or clotting factor concentrates to stop active bleeding.
What surprises most people is how long treatment lasts. Because bromadiolone is highly fat-soluble, it lodges in the liver and releases slowly over weeks or months. The average treatment duration in one clinical study was 168 days, with a median of 140 days. Some patients required vitamin K1 for as long as two years. Doses during maintenance treatment typically ranged from 10 to 120 mg per day, with most patients receiving around 100 mg daily by mouth. The dose is gradually tapered while doctors monitor clotting function through blood tests.
The Problem of Secondary Poisoning
Bromadiolone doesn’t just kill the rodent that eats it. Because the poison accumulates in the liver and takes days to kill, a poisoned rat becomes a toxic meal for any predator that catches it. This secondary poisoning is one of the most significant environmental concerns with second-generation rodenticides.
A global review of anticoagulant rodenticide exposure in non-target animals found bromadiolone in 30% of over 4,500 wildlife samples tested. Raptors are especially vulnerable. Lethal concentrations in birds of prey start at roughly 100 to 200 micrograms per kilogram of liver tissue, and field studies have documented levels far exceeding that threshold: 490 micrograms per kilogram in a red kite, 679 in a kestrel, and over 1,000 in both barred owls and great horned owls. Eagles, including golden eagles and Eurasian eagle owls, have also tested positive at dangerous levels.
The exposure pathway extends beyond rodents. Bromadiolone residues have been detected in non-target mammals, reptiles, invertebrates, and marine life. These animals serve as prey for raptors, creating multiple routes of exposure that compound the problem beyond direct rodent consumption.
Environmental Persistence
In soil, bromadiolone breaks down relatively quickly under the right conditions. Studies show 45 to 78% degrades within the first 21 days, and it binds tightly to the top three centimeters of soil rather than leaching deeper. Water is another story. Bromadiolone’s half-life in water is 392 days, meaning it takes over a year for just half the compound to break down. It is moderately to very highly toxic to fish and other aquatic organisms, making contamination of waterways a genuine concern.
Regulations on Consumer Use
The U.S. Environmental Protection Agency has restricted how bromadiolone and other second-generation anticoagulant rodenticides can be sold. These products are no longer registered for consumer use. Only licensed commercial and structural pest control professionals can purchase and apply them. Consumer-market rodenticide products are limited to ready-to-use bait stations containing first-generation compounds in block or paste form. Loose pellet baits have also been removed from the consumer market entirely.
These restrictions were driven by the documented risks to children, pets, and wildlife. Professional applicators are required to use tamper-resistant bait stations and follow label directions designed to minimize non-target exposure.
Growing Resistance in Rodent Populations
The same evolutionary pressure that made first-generation rodenticides less effective is now emerging with second-generation compounds, including bromadiolone. Resistance develops through mutations in the gene that codes for the vitamin K recycling enzyme, the same enzyme bromadiolone targets. Researchers have identified specific mutations in both rats and mice across multiple countries. A study in Lebanon found several previously undocumented mutations in local rodent species, and the Rodenticide Resistance Action Committee maintains global maps tracking where resistance has been confirmed.
The practical consequence is a troubling cycle: as resistance spreads, pest controllers may increase bait quantities or switch to even more potent compounds, which amplifies the risks to non-target species. Researchers studying resistance patterns now recommend that pest control practitioners test local rodent populations and choose compounds accordingly rather than relying on a single product.