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Pet Owner Version

Poisoning from Human Over-the-Counter Drugs


Safdar A. Khan

, DVM, MS, PhD, DABVT, ASPCA Animal Poison Control Center, Urbana, Illinois

Reviewed/Revised Oct 2020 | Modified Nov 2022

Safety of most over-the-counter human drugs or nutritional supplements has not been determined in animals; however, some are known to cause toxicity. Be sure to discuss the potential risks of using over-the-counter medications with your veterinarian before intentionally giving them to your pet. Store all medicines where your pet cannot reach them to avoid accidental ingestion.


Antihistamines provide symptomatic relief of allergic signs (such as itchiness, hives, and difficulty breathing) caused by release of histamine in the body. Antihistamines are often combined with other ingredients in many over-the-counter cold, sinus, and allergy medications. Commonly used antihistamines include chlorpheniramine, dimenhydrinate, diphenhydramine, promethazine, meclizine, and loratadine. Depending on the dose and the amount of time since ingestion, signs of antihistamine toxicity can include depression or hyperactivity, drooling, rapid breathing, rapid heartbeat, gastrointestinal upset, lack of coordination, tremors, fever, and seizures.

Treatment of antihistamine poisoning is primarily supportive. Vomiting should be considered only if the animal is not showing any signs. Fluids and other medications are used to support cardiovascular function and control seizures.


Several types of decongestants are available as over-the-counter drugs. The decongestants most toxic to pets are discussed below.

Imidazoline Decongestants

Oxymetazoline, xylometazoline, tetrahydrozoline, and naphazoline are derivatives of imidazoline that are found in over-the-counter decongestants. They are generally used in the nose and eyes for temporary relief of nasal congestion due to colds, allergies, or sinusitis.

In dogs, signs of poisoning may include vomiting, slow heart rate, abnormal heart rhythms, low or high blood pressure, panting, increased breathing sounds, depression, weakness, nervousness, hyperactivity, or shaking. Decongestants are absorbed rapidly, and these signs appear within 30 minutes to 4 hours after exposure. The gastrointestinal tract, heart, lungs, and nervous system can be affected.

Fluids are given to support heart function and to correct metabolic abnormalities, along with other medications to correct the heart rate and control apprehension and shaking. Yohimbine, a drug that cancels out the effect of the antihistamine on the body, can also be used.

Pseudoephedrine and Ephedrine

Ephedrine and pseudoephedrine are common over-the-counter medications used as nasal decongestants. Pseudoephedrine is found naturally in plants of the genus Ephedra. These drugs are not affected by the current Food and Drug Administration ban on products containing ephedra; in many areas, however, products containing pseudoephedrine are now kept behind the pharmacy counter due to their possible use in creating methamphetamine.

Pseudoephedrine and ephedrine overdose can result in enlarged pupils, rapid heartbeat, high blood pressure, abnormal heart rhythms, agitation, anxiety, hyperactivity, tremors, head bobbing, hiding, vomiting, and death. Treatment consists of removing any drug that has not been absorbed, controlling the central nervous system and cardiovascular effects, and supportive care. Vomiting should be induced or the stomach should be flushed, followed by administration of activated charcoal with a medicine that causes the emptying of the bowels. Hyperactivity, nervousness, seizures, and rapid heartbeat should be controlled through medication. Fluids should be given. Signs can last 1 to 4 days.

Pseudoephedrine is being replaced by phenylephrine as a decongestant in oral forms, nasal sprays, and eye drops. Effects such as agitation, nervousness, and high blood pressure may occur less frequently. Treatment is mainly supportive, similar to pseudoephedrine poisoning.

Nonsteroidal Anti-inflammatory Drugs (NSAIDs)

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most commonly used class of human medications in the world. Due to their widespread availability and use, human NSAIDs are often accidentally ingested by dogs and cats. Ibuprofen, aspirin, naproxen, and acetaminophen are some of the most common NSAIDs. These drugs should not be used in pets unless directed by your veterinarian.

Treatment of NSAID poisoning consists of removing any drug that has not been absorbed, protecting the gastrointestinal tract and kidneys, and providing supportive care. Vomiting should be induced in recent exposures, followed by administration of activated charcoal with a medication that empties the bowels. Fluids are given to increase urine output. The outlook for recovery depends on the amount ingested and the amount of time between ingestion and treatment.

Ibuprofen is used for its anti-inflammatory, fever-reducing, and pain-relieving properties in animals and people. It is rapidly absorbed after ingestion, but food in the stomach can slow this process. Ibuprofen can be used in dogs, but it has a narrow margin of safety. Prolonged use can cause stomach ulcers and perforations, as well as kidney damage. In addition, central nervous system depression, low blood pressure, lack of coordination, heart effects, seizures, coma, and death can be seen. A single ingestion can lead to sudden and severe vomiting, diarrhea, abdominal pain, and loss of appetite.

Cats are more sensitive to ibuprofen than dogs, and toxicosis is seen at only half the dosage that causes problems in dogs. Ibuprofen toxicity is more severe in ferrets than in dogs that consume similar dosages.

Aspirin is rapidly absorbed from the gastrointestinal tract in animals. Aspirin poisoning is usually characterized by depression, fever, unusually deep or fast breathing, seizures, metabolic abnormalities, coma, stomach irritation or ulceration, liver damage, or increased bleeding time. Large dosages can be fatal in cats. Dogs tolerate aspirin better than cats, but prolonged use can result in stomach ulcers.

Naproxen is available as tablets, gelcaps, and as a suspension. Naproxen is similar to carprofen and ibuprofen. In people and dogs, naproxen is used for its anti-inflammatory, pain-relieving, and fever-reducing properties. It is rapidly absorbed after ingestion. Naproxen poisoning in dogs has caused bleeding into the bowels. Signs include black feces, frequent vomiting, abdominal pain, perforating ulcer of the small intestine, weakness, stumbling, pale mucous membranes, and anemia. Cats may be even more sensitive to naproxen toxicity than dogs.

Acetaminophen is commonly used in people to reduce fever and relieve pain. It has a lower risk of stomach ulceration than aspirin. Acetaminophen is rapidly absorbed, but absorption can be delayed with extended-release formulations. In dogs, signs of toxicity are usually not seen unless the dosage of acetaminophen is very high. Toxicity can be seen at lower dosages with repeated exposures. Cats are more sensitive to acetaminophen, and toxicity is seen at much lower dosages than in dogs.

Acetaminophen poisoning is characterized by changes in the hemoglobin in the blood and damage to the liver. Kidney damage is also possible. Cats primarily develop the changed hemoglobin in the blood within a few hours, resulting in a condition called Heinz body anemia. This results in mucous membranes becoming brown or muddy in color, and is usually accompanied by a rapid heartbeat, unusually deep or fast breathing, weakness, and lethargy. Other signs include depression, weakness, jaundice, vomiting, dangerously low body temperature, fluid buildup within the face or paws, a bluish tinge to the skin and mucous membranes, liver damage, and death.

Treatment of acetaminophen poisoning includes removing drug that has not been absorbed from the stomach, preventing or treating the blood changes and liver damage, and providing supportive care. Inducing vomiting is useful when performed early, followed by administration of activated charcoal with a medication that empties the bowels. Fluids and blood transfusions are given as needed.

Gastrointestinal Drugs

H2-receptor antagonists, also called H2 blockers, are commonly used to treat gastrointestinal ulcers, inflammation of the esophagus, and gastric reflux (a backward flow of stomach contents). Cimetidine, famotidine, and ranitidine are examples of this group. These drugs are rapidly absorbed, reaching peak blood concentrations within 1 to 3 hours.

H2 blockers have a wide margin of safety. Overdoses typically result in minor effects such as vomiting, diarrhea, loss of appetite, and dry mouth. Treatment generally consists of monitoring and supportive care.

Antacids come in pill and liquid forms, and are frequently used to treat gastrointestinal upset. Common antacids include calcium carbonate, aluminum hydroxide, and magnesium hydroxide (milk of magnesia). These agents are poorly absorbed when ingested by mouth. Calcium- and aluminum-containing antacids generally cause constipation, while magnesium-containing antacids tend to cause diarrhea. Some products contain both aluminum and magnesium salts in an attempt to balance their constipating and laxative effects. Ingestion of calcium salts may cause a temporary excess of calcium in the blood, but significant whole-body effects are unlikely. Inducing vomiting within 2 to 3 hours of exposure may be helpful in preventing severe gastrointestinal upset.

Multivitamins and Iron

The common ingredients in multivitamins include ascorbic acid (vitamin C), cyanocobalamin (vitamin B12), folic acid, thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), biotin, pantothenic acid, pyridoxine (vitamin B6), calcium, phosphorus, iodine, iron, magnesium, copper, zinc, and vitamins A, D, and E. Among these ingredients, iron and vitamins A and D may cause significant problems if overdosed. Ingestion of large amounts of the other ingredients in pets can result in gastrointestinal upset (for example, vomiting, diarrhea, loss of appetite) that resolves on its own. However, toxicity is typically rare in pets.

Iron has direct corrosive or irritant effects on the lining of the gastrointestinal tract. It can also be a direct poison to liver cells. Signs of iron toxicosis usually develop within 6 hours. Initial vomiting and diarrhea, with or without blood, may be followed by shock, depression, fever, metabolic abnormalities, and liver failure 12 to 24 hours later, often with a period of apparent recovery in between. Shock may lead to kidney failure. An overdose of iron generally warrants inducing vomiting (or flushing the stomach), administering gastrointestinal protectants, and providing supportive treatment.

Vitamin A toxicity is not likely to occur after ingesting multivitamins. The amount of vitamin A needed to cause toxic effects is 10 to 1,000 times the dietary requirements for most species. Vitamin A toxicity after consumption of large amounts of fish oil or bear's liver has been well documented. Signs associated with vitamin A toxicity include general malaise, loss of appetite, peeling skin, weakness, tremors, convulsions, paralysis, and death.

Vitamin D is included in many calcium supplements to aid the absorption of the calcium. Most vitamins contain cholecalciferol (vitamin D3). Vomiting, depression, passing large amounts of urine, excessive thirst, and high levels of phosphate in the blood may be seen within 12 hours, followed by high levels of calcium in the blood and sudden kidney failure 1 to 2 days after exposure. In addition to kidney failure, the heart and gastrointestinal tract may show signs of damage and mineralization. Initial treatment should include inducing vomiting (or flushing the stomach) and an analysis of the blood. Multiple doses of activated charcoal with a drug that empties the bowels should be given. If signs of toxicosis develop, treatment includes fluids and medications to increase urine output and to bind phosphate. Stabilization of blood calcium may require many days of treatment.

Herbal Supplements

Guarana (Paullinia cupana), a natural source of caffeine, and ma huang (Ephedra sinica), a natural source of ephedrine, are contained in several herbal supplements that claim to help people lose weight and improve their energy level. In people, use of herbal supplements containing guarana and ma huang have been linked to inflammation of the liver (hepatitis), kidney stones, inflammation of the heart, and sudden death. In dogs, accidental ingestion of herbal supplements containing ma huang and guarana can lead to severe hyperactivity, tremors, seizures, vomiting, a rapid heartbeat, fever, and death within a few hours of exposure. The use of ephedra-containing supplements has been banned by the Food and Drug Administration. ( See also Pseudoephedrine and Ephedrine Pseudoephedrine and Ephedrine Safety of most over-the-counter human drugs or nutritional supplements has not been determined in animals; however, some are known to cause toxicity. Be sure to discuss the potential risks of... read more .)

5-Hydroxytryptophan or Griffonia seed extracts are contained in several over-the-counter herbal supplements that claim to treat depression, headaches, insomnia, and obesity. It is an amino acid that is used by the body to make the neurotransmitter serotonin. When taken by mouth, 5‑hydroxytryptophan is rapidly absorbed. Signs can develop within 4 hours after ingestion and last up to 36 hours. Signs include seizures, depression, tremors, lack of coordination, vomiting, diarrhea, fever, temporary blindness, and death. Treatment consists of inducing vomiting (or flushing the stomach), administering fluids and medications to control central nervous system signs, and regulating body temperature (cool water bath, fans). Cyproheptadine, a drug that cancels out the effects of 5-hydroxytryptophan overdosage, may be used.

Topical Zinc Oxide

Zinc oxide ointments or creams are commonly used as topical skin protectants, astringents, and bactericidal agents. Most ointments contain 10 to 40% zinc oxide. Ingestion of these products by pets usually results in vomiting, diarrhea, and liver and kidney damage. Signs are usually seen within 2 to 4 hours. Treatment is symptomatic and supportive.

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