Bromethalin: Uses, Health Effects, Safety and Regulation

Bromethalin is a neurotoxic rodenticide that damages the central nervous system. It works after the body turns it into an active metabolite. It is used in poisonous baits because no known target species tolerance exists. Unintentional exposures are rarely toxic to people, and 96.38% of pediatric exposures had no effect. It is toxic to cats and dogs, and it can bioaccumulate in hawks and owls. After an exposure, follow the steps in the article. Diagnosis starts with bait exposure followed by neurological signs within 1 to 7 days. It is regulated through registration with the US Environmental Protection Agency, and the article also lists safer use steps.

What Is Bromethalin?

Bromethalin is a neurotoxic rodenticide that damages the central nervous system. Bromethalin is a nonanticoagulant bait poison built to kill after a single ingested dose. Baits come as blocks, soft baits, pellets, worms and seed at 0.01% to 0.025% bromethalin.

In 2026, the National Pesticide Information Center at Oregon State University considers bromethalin a single-dose rodenticide. At the cell level, bromethalin disrupts energy production.

How Does Bromethalin Work?

Bromethalin begins to work after the body metabolizes it into n-desmethyl-bromethalin, an active metabolite. Bromethalin is lipid soluble, so it reaches the brain and inhibits oxidative phosphorylation there. The metabolite disrupts energy production in brain cells by uncoupling oxidative phosphorylation and lowering ATP synthesis. Disrupted sodium-potassium pumps then cause intramyelinic fluid accumulation and cerebral edema. Fluid buildup raises intracranial pressure and permanently damages neuronal axons.

In 2026, Merck & Co., Inc. states that cerebral edema and neurological dysfunction appear in a dose-dependent manner. Guinea pigs are uniquely resistant to bromethalin, which is why toxicity differs between species.

Where Is Bromethalin Used?

Bromethalin is used in poisonous baits because no known target species tolerance exists. Bromethalin baits target house mice, moles and rats in homes and gardens.

Bromethalin home and garden products were registered in California in July 2013. Health Canada, the Canadian federal health agency, restricts how bromethalin baits may be placed.

Pest management professionals in Massachusetts used bromethalin products in 2017, Tufts University noted in 2023. Children and pets meet the bait because it attracts them.

Bromethalin use grew after the EPA tightened the rules around the sale of anticoagulant rodenticides in 2008. Some consumer rodent poisons then switched from an anticoagulant to bromethalin.

How Toxic Is Bromethalin to People?

Bromethalin is rarely toxic to people in unintentional exposures, and 96.38% of pediatric exposures had no effect. Bromethalin carries a high oral and inhalation toxicity rating and a moderate dermal rating. Most unintentional exposures, such as licking a pellet, show no serious effects in children.

A 2019 study by Ryan Feldman analyzed 2674 bromethalin exposures reported to US poison centers from 2008 to 2017. Pediatric patients had no major clinical effects and no deaths.

Bromethalin ingestion for self-harm carries significant risk of death or severe neurologic effects.

What Are the Symptoms of Bromethalin Poisoning in People?

Bromethalin poisoning in people causes symptoms that begin in the gut and can reach the nervous system. The most common initial effects of unintentional exposure are nausea, vomiting, abdominal pain and diarrhea. Key symptoms include:

• Nausea: Nausea is a common initial effect of unintentional exposure. It belongs to the mostly minor, self-limited gastrointestinal upset.
• Vomiting: Vomiting is a common initial effect of unintentional exposure. Like nausea, it sits in the minor gastrointestinal group of effects.
• Abdominal pain: Abdominal pain is a common initial effect of unintentional exposure. It forms part of the self-limited gastrointestinal upset.
• Diarrhea: Diarrhea is a common initial effect of unintentional exposure. It completes the gastrointestinal picture that most patients show.
• Delayed seizures: Delayed seizures have been reported in humans. They are a late effect, unlike the early gastrointestinal upset.
• Paralysis: Paralysis is a nervous system effect of damage to the central nervous system. It marks the severe end of the range, which can end in death.
• Convulsions: Convulsions are a nervous system effect of damage to the central nervous system. Edema and ion-pump disruption cause diffuse spongiosis of the white matter in humans.

A 2016 study by Serena Huntington reviewed 129 human calls to the California Poison Control System from 1997 to 2014. Adverse effects were minor, self-limited and mostly gastrointestinal upset. Minor outcomes occurred in 7.9% of patients.

How Soon After Exposure Do Bromethalin Symptoms Appear?

Bromethalin symptoms appear as soon as 4 hours after exposure and as late as 7 days. Bromethalin delays fatal toxicity by hours to days, because an active metabolite must form. In dogs at toxic doses, the convulsant syndrome appears within 4 to 36 hours.

In 2013, the Canadian Veterinary Journal noted that signs occur in 1 to 7 days. They progressively increase over 1 to 2 weeks.

How Toxic Is Bromethalin to Dogs and Cats?

Bromethalin is toxic to cats and dogs, and 60% of cats versus 25% of dogs had confirmed exposure. Bromethalin leaves cats exquisitely sensitive, while dogs are moderately sensitive.

In 2025, Sigal Klainbart reviewed 223 cases from 2010 to 2023 at a California laboratory. Cats were more likely to have confirmed desmethylbromethalin exposure.

Bromethalin causes the paralytic syndrome in cats irrespective of the dose.

What Are the Signs of Bromethalin Poisoning in Dogs and Cats?

Bromethalin poisoning in dogs and cats produces signs that range from hyperexcitability to paralysis. Key signs include:

• Hyperexcitability: Hyperexcitability is a convulsant sign in dogs. It shows as extreme sensitivity to being touched, with seizures triggered by light or noise.
• Muscle tremors: Muscle tremors are a convulsant sign in dogs. They appear within the same syndrome as the seizures.
• Grand mal seizures: Grand mal seizures are a convulsant sign in dogs. They are among the most serious signs recorded.
• Hindlimb hyperreflexia: Hindlimb hyperreflexia is a convulsant sign in dogs. It is listed with the other convulsant signs.
• CNS depression: CNS depression is a convulsant sign in dogs. It shows that the central nervous system is affected.
• Hyperthermia: Hyperthermia is a raised body temperature listed among the signs of bromethalin poisoning. Its timing and frequency are not reported in the sources.
• Paralysis in cats: Paralysis in cats is the paralytic form, which appears 1 to 7 days after exposure and progresses over 1 to 2 weeks. Signs may persist for weeks and rarely become a mild permanent deficit.

A study in the Journal of Veterinary Internal Medicine by Sigal Klainbart recorded seizures, tremors, weakness and paralysis. Bromethalin damage to the brain explains why the signs appear.

How Much Bromethalin Is Lethal to Cats and Dogs?

Published LD50 values for bromethalin range from 2.38 to 4.7 mg/kg in dogs. Bromethalin is lethal to cats at an LD50 of 0.4 to 0.71 mg/kg, so cats need much less.

The average LD50 of about 3.54 mg/kg is the convulsant threshold in dogs.

A 2021 study by Katherine M Scotti recorded a median ingested dose of 0.2 mg/kg in 59 dogs.

Bromethalin toxic doses are accepted at one-tenth of the lowest reported LD50 in companion animal species. Cats carry the lower LD50, which explains their greater sensitivity.

Is Bromethalin Dangerous to Birds and Wildlife?

Yes. Bromethalin is dangerous to birds and wildlife because it can bioaccumulate in hawks and owls.

Maureen Murray of the Department of Infectious Disease and Global Health reported desmethylbromethalin in 29.5% of 44 hawks and owls. The birds were sampled in Massachusetts from 2021 to 2022. Anticoagulant residues were present in 95.5% of the same birds.

The Tufts Wildlife Clinic led the 2023 sampling of bromethalin in hawks and owls. Nontarget species are typically exposed by unintended direct ingestion of bait. Detection shows exposure, which is not the same as confirmed death.

Can Bromethalin Cause Secondary Poisoning?

It depends. Bromethalin can cause secondary poisoning in theory when animals eat animals that ingested it. Relay toxicosis after eating prey or carrion has not been documented in research settings.

In 2023, Maureen Murray, director of the Tufts Wildlife Clinic, led studies of bromethalin in raptors.

A 2023 study by Maureen Murray in the Journal of Wildlife Diseases supports the possibility of secondary bromethalin toxicosis.

Bromethalin studies that prove or disprove this type of secondary poisoning do not yet exist. Predators and scavengers that eat the prey are the animals that could be exposed.

What Should Be Done After Bromethalin Exposure?

To know what should be done after bromethalin exposure, follow the 4 steps below.

1. Take the person or animal for care immediately. Animals that ingest bromethalin need immediate emergency veterinary care. Early action matters because signs can be delayed.
2. Call the Poison Control Center at 800-222-1222 for case advice. All human cases should be managed in consultation with a poison control center. The line gives treatment advice for United States cases.
3. Decontaminate early, before symptoms appear. Emesis is induced if ingestion occurred within 4 hours, and activated charcoal at 1 to 2 g/kg is repeated. Once clinical signs develop, treatments and supportive care are generally ineffective.
4. Monitor electrolytes, especially sodium, after activated charcoal. Sodium is monitored after charcoal and cathartics. Monitoring supports care but is not an antidote.

Katherine M Scotti of the Michigan State University Veterinary Medical Center recorded decontamination in 179 dogs. Emesis induction was used in 14 dogs, activated charcoal in 42 and both in 123.

Bromethalin decontamination before symptoms appear is the main protective step in the sources.

Is There an Antidote for Bromethalin Poisoning?

No. No antidote for bromethalin poisoning is known, and care is symptomatic and supportive.

Ryan Feldman of the Wisconsin Poison Center found that no antidote is available.

Bromethalin signs, once they develop, make treatments and supportive care generally ineffective. Corticosteroids are controversial and unlikely to help bromethalin-induced cerebral edema.

How Is Bromethalin Poisoning Diagnosed?

To see how bromethalin poisoning is diagnosed, start with bait exposure followed by neurological signs within 1 to 7 days. Collect liver, kidney, brain or fat for confirmation, because confirmation requires detecting bromethalin or its metabolite. Choose fat first, since fat is the best tissue for finding desmethylbromethalin. Expect nonspecific results, since cerebrospinal fluid pressure may or may not be raised and necropsy findings are nonspecific. Rule out marijuana, benzodiazepines, opiates and ethylene glycol.

Sigal Klainbart of the University of California reported that adipose tissue remains the most reliable sample for diagnosis.

How Is Bromethalin Regulated in the United States?

Bromethalin is regulated in the United States through registration with the US Environmental Protection Agency. The US Environmental Protection Agency, which registers pesticides and runs their registration review, first registered bromethalin in 1984.

The 2008 rules followed exposures among children, pets and non-target wildlife. They took partial effect in 2011.

In 2022, the US Federal Register published an EPA notice of proposed interim decisions on rodenticides including bromethalin. The notice opens a 75-day public comment period.

How Can Bromethalin Be Used More Safely?

To see how bromethalin can be used more safely, follow the 4 steps below.

1. Read the product label before use. The label gives specific information on personal protective equipment and safety requirements. It costs little time and sets the PPE rules.
2. Wear basic PPE such as chemical-resistant gloves, long sleeves and goggles. This basic PPE is advised for handling bait. The label can name further requirements.
3. Place bait where children and pets cannot reach it. Bait is attractive to children and pets, so it must never be used or stored within their reach.
4. Use tamper-resistant bait stations. Stations make accidents harder to cause. They do not replace out-of-reach placement.

In 2026, the UC Statewide IPM Program advises readers to check the product label for specific PPE and safety requirements. Children and pets face the highest risk, because the bait is attractive to them.