Substances Poisonous to Dogs: A Complete Toxicology Reference

Accidental poisoning is one of the most common emergencies in companion animal medicine. The ASPCA Animal Poison Control Center managed 401,550 cases in 2023, the most recent year with published data. The top categories of exposure were over-the-counter medications, prescription medications, food items, chocolate, and plants.

Toxicity is fundamentally a question of dose per kilogram of body weight. A substance that causes mild stomach upset in a large-breed dog may produce life-threatening effects in a toy breed exposed to the same absolute amount. Individual sensitivity, pre-existing health conditions, and whether the dog has eaten recently also influence how a poisoning unfolds.

Time to treatment is the single most important variable in most poisoning cases. Decontamination — removing the toxin from the body before it is fully absorbed — is most effective in the first one to two hours. After that window, treatment shifts to antidotes where available, symptomatic support, and monitoring for organ damage.

This reference covers the major categories of substances toxic to dogs, with dose thresholds where published data exist, clinical signs organized by body system, and emergency management principles. It is intended as an informational resource, not a substitute for professional veterinary advice. Any suspected poisoning warrants an immediate call to your vet or a veterinary poison control service.

Chocolate and Theobromine

Chocolate toxicity in dogs is caused by methylxanthines, primarily theobromine and to a lesser extent caffeine. Dogs metabolize theobromine much more slowly than humans, with a half-life of approximately 17.5 hours in dogs compared to 6-10 hours in people.

Toxic dose thresholds for theobromine are approximately:

• Mild signs (vomiting, diarrhea, restlessness): 20 mg/kg body weight
• Cardiac signs (tachycardia, arrhythmias): 40-50 mg/kg
• Seizures and severe toxicity: 60+ mg/kg

Theobromine content varies widely by chocolate type:

• White chocolate: ~0.25 mg/g (very low risk from theobromine, but fat content can cause pancreatitis)
• Milk chocolate: 1.5-2 mg/g
• Dark chocolate (60-70%): 5-8 mg/g
• Baking chocolate (unsweetened): 13-16 mg/g
• Dry cocoa powder: 14-26 mg/g

A 10 kg dog eating 50 grams of dark chocolate (approximately 2 ounces) could ingest 250-400 mg of theobromine, putting it well into the cardiac-risk range.

Grapes and Raisins

Tartaric acid has been identified as the likely nephrotoxic agent in grapes and raisins, based on research published in 2021. However, no reliably safe dose has been established. Some dogs develop acute kidney injury after eating a single grape, while others have tolerated larger amounts without apparent harm. This unpredictable individual variation means any grape or raisin ingestion in a dog should be treated as potentially dangerous.

Kidney injury typically develops within 24-72 hours of ingestion. Early signs include vomiting, decreased appetite, lethargy, and abdominal pain, progressing to reduced urine output and kidney failure in severe cases. Raisins, grape juice concentrates, and currants carry the same risk.

Xylitol (Birch Sugar)

Xylitol triggers a potent insulin release in dogs that does not occur in humans. This can cause dangerously low blood sugar (hypoglycemia) within 10-60 minutes of ingestion.

• Hypoglycemia risk: doses above 0.1 g/kg body weight
• Hepatotoxicity risk: doses above 0.5 g/kg body weight

A single piece of sugar-free gum may contain 0.3-1.0 grams of xylitol, enough to cause hypoglycemia in a small dog. Xylitol is found in sugar-free gum and candy, some peanut butters, dental products, baked goods, chewable vitamins, and nasal sprays. It may also be labeled as birch sugar.

Allium Species (Onion, Garlic, Leeks, Chives)

All members of the Allium family cause oxidative damage to red blood cells, leading to Heinz body formation and hemolytic anemia. Toxic doses are generally reported as:

• Onions: ingestion of more than 15-30 g/kg body weight
• Garlic: historically considered more potent per gram, but toxic dose ranges overlap with onion at roughly 15-30 g/kg depending on the source

All forms are toxic: raw, cooked, powdered, dehydrated, and in sauces or baby food. Signs of anemia (pale gums, weakness, rapid breathing, dark urine) may not appear for several days after ingestion because red blood cell destruction is a delayed process.

Macadamia Nuts

The toxic mechanism of macadamia nuts in dogs remains unknown. Toxic effects have been reported at doses of 2.4-62.4 g/kg body weight. Signs typically appear within 12 hours and include weakness (especially hind limb), vomiting, hyperthermia, and tremors.

Macadamia nut toxicity is generally self-limiting, with most dogs recovering within 24-48 hours with supportive care. However, combined ingestion with chocolate (as in chocolate-covered macadamia nuts) creates compounded risk and should be treated more urgently.

Alcohol and Ethanol

Dogs are significantly more sensitive to ethanol than humans. The toxic dose is approximately 5.5-6.5 mL/kg of 100% ethanol. Sources of ethanol exposure include alcoholic beverages, rum-soaked cakes and desserts, fermenting bread dough (which produces ethanol in the stomach), hand sanitizer, and certain medications or extracts.

Bread dough is a particular concern because it continues to ferment and expand in the warm, acidic environment of the stomach, producing increasing amounts of ethanol while also risking gastric obstruction.

Human medications are consistently among the top categories reported to animal poison control. Many common over-the-counter and prescription drugs are far more dangerous to dogs than pet parents expect.

NSAIDs (Ibuprofen, Naproxen)

Non-steroidal anti-inflammatory drugs cause dose-dependent toxicity in dogs:

• GI ulceration: 25-125 mg/kg ibuprofen
• Renal failure: 175-300 mg/kg
• CNS toxicity (seizures, coma): doses exceeding 400 mg/kg

A single 200 mg ibuprofen tablet can produce toxic effects in a dog weighing less than 8 kg (about 18 pounds). Naproxen has a longer half-life in dogs than ibuprofen and carries similar risks at lower doses. Dogs should never be given human NSAIDs; veterinary-specific NSAIDs have different safety profiles.

Acetaminophen (Paracetamol)

Acetaminophen causes hepatotoxicity in dogs at doses of 75-100 mg/kg. At higher doses, it can also cause methemoglobinemia, a condition where hemoglobin loses its ability to carry oxygen effectively. While cats are far more sensitive to acetaminophen than dogs, it remains dangerous for dogs and should never be administered without veterinary guidance.

The antidote N-acetylcysteine is effective when given early but must be administered under veterinary supervision.

Antidepressants (SSRIs, SNRIs, TCAs)

Antidepressants are the number one category of prescription medication poisoning in pets. Ingestion can cause serotonin syndrome, characterized by agitation, tremors, hyperthermia, rapid heart rate, dilated pupils, and seizures. Tricyclic antidepressants (TCAs) additionally carry risk of cardiac conduction abnormalities.

Dogs may be attracted to pill bottles or blister packs. Even a single pill of some antidepressants can be toxic to a small dog.

ADHD Medications (Amphetamines, Methylphenidate)

Stimulant medications cause cardiac stimulation and CNS excitation in dogs. Signs include hyperactivity, tremors, seizures, elevated heart rate, high blood pressure, and hyperthermia. A single pill of extended-release formulations can be life-threatening for small dogs because the drug is released over many hours.

Pseudoephedrine and Phenylephrine

These sympathomimetic decongestants, found in many cold and sinus medications, cause agitation, hyperactivity, elevated heart rate, and potentially seizures in dogs. Combination cold products may also contain acetaminophen or NSAIDs, compounding the toxicity.

Hundreds of plants are toxic to dogs, but a handful account for the majority of serious poisoning cases. Toxicity varies by plant part, season, and amount ingested.

Sago Palm (Cycas revoluta)

Sago palm is one of the most dangerous plants for dogs. All parts are toxic, but the seeds (nuts) contain the highest concentration of cycasin, a potent hepatotoxin. Even small ingestions can cause severe liver necrosis. The mortality rate is 50-75% even with aggressive treatment, making this one of the deadliest plant exposures in veterinary medicine.

Signs develop within hours to days and include vomiting, bloody diarrhea, jaundice, liver failure, and coagulopathy.

Oleander (Nerium oleander)

All parts of the oleander plant contain cardiac glycosides that can cause fatal cardiac arrhythmias. Toxicity has been reported from chewing leaves, drinking water from vases containing oleander cuttings, and even from inhaling smoke when oleander is burned. Dogs do not need to swallow large amounts for serious poisoning to occur.

Autumn Crocus (Colchicum autumnale)

Not to be confused with the less toxic spring crocus, the autumn crocus contains colchicine, which can cause severe multi-organ failure. Initial GI signs (vomiting, bloody diarrhea) may be followed by bone marrow suppression, liver damage, respiratory failure, and death. Effects can be delayed, appearing 24-72 hours after ingestion.

Lilies (Lilium and Hemerocallis Species)

Lilies are primarily a severe nephrotoxic threat to cats, where even small exposures to pollen or water from a lily vase can cause fatal kidney failure. In dogs, lily ingestion more commonly causes gastrointestinal irritation (vomiting, drooling, decreased appetite) but is far less likely to cause renal failure. Peace lilies and calla lilies (Araceae family) cause oral irritation in both species but are a separate and generally less dangerous category.

Rhododendron and Azalea

These popular landscaping plants contain grayanotoxins that affect sodium channels in cell membranes. Ingestion can cause vomiting, drooling, diarrhea, weakness, cardiac arrhythmias, hypotension, and in severe cases, coma or death.

Tulip and Hyacinth Bulbs

The bulbs contain the highest concentration of allergenic lactones and similar compounds. Dogs that dig up and chew bulbs can develop intense oral irritation, drooling, vomiting, and diarrhea. Severe ingestions may cause cardiac and respiratory changes.

Antifreeze (Ethylene Glycol)

Ethylene glycol is among the most dangerous household toxins for dogs. The lethal dose is approximately 4.4-6.6 mL/kg in dogs. Its sweet taste makes it attractive to animals, and even small puddles from a leaking radiator can contain a fatal dose for a small dog.

After ingestion, ethylene glycol is metabolized by alcohol dehydrogenase into glycolic acid and oxalic acid, which cause severe metabolic acidosis and calcium oxalate crystal deposition in the kidneys, leading to acute renal failure. The antidote fomepizole (4-MP) must be administered within 8-12 hours of ingestion to be effective, as it works by blocking the metabolic conversion. Ethanol can be used as an alternative antidote when fomepizole is unavailable.

Propylene glycol-based antifreeze products are significantly less toxic and are sometimes marketed as pet-safer alternatives, though they are not completely without risk.

Rodenticides

Rat and mouse poisons represent a particularly complex category because multiple classes exist with entirely different mechanisms of toxicity:

• Anticoagulant rodenticides (warfarin, bromadiolone, brodifacoum): Inhibit vitamin K-dependent clotting factors. Signs of bleeding may not appear for 3-5 days. Treatment is vitamin K1 therapy for 30+ days for second-generation compounds.
• Bromethalin: Causes cerebral edema and neurological signs (tremors, seizures, paralysis). No specific antidote exists; treatment is decontamination and supportive care.
• Cholecalciferol (vitamin D3): Causes severe hypercalcemia and mineralization of soft tissues including kidneys. Even small amounts can be very dangerous.
• Zinc phosphide: Reacts with stomach acid to produce toxic phosphine gas. Causes severe GI distress, cardiovascular collapse, and liver damage.

Identifying the active ingredient is critical because treatment differs completely between types. Always bring the packaging to the vet.

Cleaning Products

Alkaline products such as drain cleaners, oven cleaners, and dishwasher pods are corrosive and can cause chemical burns to the mouth, esophagus, and stomach. Vomiting should never be induced after ingestion of corrosive substances because it causes additional damage.

Household bleach (sodium hypochlorite at typical household concentrations of 3-8%) generally causes gastrointestinal irritation rather than severe chemical burns, though concentrated industrial bleach is more dangerous.

Heavy Metals (Lead, Zinc)

Lead toxicity most commonly occurs from ingestion of lead paint chips (in older homes), fishing sinkers, lead-containing toys, or contaminated soil. Chronic low-level exposure causes GI signs, neurological abnormalities, and behavioral changes.

Zinc toxicity occurs primarily from ingestion of US pennies minted after 1982 (which contain 97.5% zinc), zinc-containing hardware, or zinc oxide ointments. Zinc causes hemolytic anemia by directly damaging red blood cell membranes. Batteries containing zinc also pose both corrosive and zinc toxicity risks.

The management of any poisoning case follows a structured approach: stabilize, decontaminate, administer antidotes when available, and provide supportive care.

Decontamination

Emesis induction (causing vomiting) is most effective within 1-2 hours of ingestion, before the toxin is fully absorbed. In a veterinary setting, apomorphine is the preferred emetic agent for dogs. Hydrogen peroxide (3%) may be recommended by poison control for at-home use in specific situations, but it should only be administered under professional guidance. Emesis is contraindicated for many substances and should never be a default action.

Activated charcoal can bind many toxins in the GI tract and reduce absorption when given within 1-2 hours of ingestion. It is not effective for all substances (notably metals, alcohols, and xylitol) and carries aspiration risk if the dog is vomiting or has decreased consciousness.

Gastric lavage (stomach pumping) is occasionally performed under general anesthesia in veterinary emergency settings for large or recent ingestions, but it is not commonly used for most cases.

Specific Antidotes

Antidotes exist for a limited number of toxins:

• Fomepizole (4-MP): Blocks metabolism of ethylene glycol. Must be given within 8-12 hours.
• Vitamin K1: Reverses effects of anticoagulant rodenticides. Requires 30+ days of oral therapy for second-generation compounds.
• N-acetylcysteine (NAC): Treats acetaminophen toxicity by replenishing glutathione and protecting the liver.
• Intralipid emulsion (ILE): Intravenous fat emulsion used for toxicity from lipophilic drugs, including some local anesthetics, calcium channel blockers, and certain other fat-soluble medications.
• Atropine: Used for organophosphate and carbamate insecticide poisoning.

Supportive Care

Most poisoning treatment is supportive, meaning it focuses on keeping the patient stable while the body processes and eliminates the toxin. Key supportive measures include:

• IV fluid therapy: Supports kidney function, corrects dehydration, and helps maintain blood pressure
• GI protectants: Sucralfate, omeprazole, or famotidine to protect the stomach and intestinal lining
• Anti-nausea medications: Maropitant (Cerenia) or ondansetron to control vomiting
• Thermoregulation: Managing hypothermia or hyperthermia
• Seizure control: Diazepam or other anticonvulsants if seizures develop
• Cardiac monitoring: Continuous ECG for toxins that affect the heart

When NOT to Induce Vomiting

Do not induce vomiting if your dog has ingested:

• Caustic or corrosive substances (drain cleaners, oven cleaners, strong acids or alkalis) — vomiting causes additional chemical burns
• Petroleum products (gasoline, kerosene, motor oil) — aspiration into the lungs is a serious risk
• Sharp objects — risk of esophageal or pharyngeal perforation
• If the dog is seizing, unconscious, or has decreased gag reflex — aspiration risk is extremely high
• If more than 2 hours have passed since ingestion — most of the toxin has already been absorbed

Always call poison control or your veterinarian before taking any action at home.

Most accidental poisonings are preventable with consistent household management and awareness.

Medications: Store all human and veterinary medications in closed cabinets, not on counters, nightstands, or in bags on the floor. Dogs can chew through pill bottles and blister packs. Weekly pill organizers are a common source of multi-drug ingestions.

Kitchen and trash: Secure trash cans with locking lids and keep compost bins inaccessible. Many food toxin exposures happen when dogs access garbage containing chocolate wrappers, coffee grounds, onion scraps, or discarded fruit. Counter-surfing dogs need particular management.

Plants: Research every plant before bringing it into your home or yard. The ASPCA maintains a searchable database of toxic and non-toxic plants. Remove sago palms, oleander, autumn crocus, and other high-risk plants from areas where your dog has access.

Food ingredients: Read ingredient labels on human foods before sharing or leaving them accessible. Xylitol (birch sugar) appears in an expanding list of products, including some peanut butters, protein bars, and baked goods. New formulations enter the market regularly.

Garage and outdoor chemicals: Store antifreeze, rodenticides, herbicides, pesticides, and fertilizers in locked storage that dogs cannot access. Clean automotive fluid spills immediately. If using rodenticides, choose pet-safe bait stations and monitor for relay toxicity (dogs eating poisoned rodents).

Childproofing as pet-proofing: Install childproof locks on lower cabinets that contain cleaning products, automotive chemicals, or medications. Dogs are often more persistent and stronger than child locks are designed for, so consider placement in upper cabinets when feasible.

Household education: Make sure all family members, roommates, pet sitters, and regular visitors understand what is dangerous to dogs. Many poisonings happen when well-meaning guests share food or leave medications within reach.