Practitioner Updates

June 2, 2026

Pharmacist’s Corner: Potential Toxicity to Animals of Human Vitamins, Supplements

Many pet owners think over-the-counter medications, vitamins, and supplements are safe, but using them incorrectly can seriously harm pets. The ASPCA reports that these products, including human pain relievers, cough and cold medicines, topical creams, and vitamin or mineral supplements, are the top cause of toxic exposures in pets, making up about 16.5% of all poison control calls.

Talking with clients about differences in product ingredients, strength, and added substances like xylitol or caffeine can help prevent accidental poisoning and keep animals safe. This summary covers commonly used vitamins and supplements and their risks in animals to help with client education and safe use.

Vitamin A and Omega-3

Vitamin A and omega-3 toxicities are commonly found in products like fish oils (e.g., cod liver oil), polar bear liver, or seal liver. When used correctly, they can help with allergies, dry or itchy skin, and arthritis in animals. Vitamin A toxicity is rare with regular supplements and only occurs if 10 to 1,000 times the recommended amount is ingested. Clinical signs of toxicity include tiredness, loss of appetite, nausea, skin peeling, weakness, tremors, seizures, paralysis, and even death. Cats are more likely than dogs to be affected.

Vitamin B

Although there are seven types of water-soluble B vitamins, toxicity is uncommon because excess amounts are filtered by the kidneys and excreted in the urine. Ingesting too much can cause stomach upset or change the color of urine. Taking too much vitamin B3 (niacin) can also cause temporary skin flushing and itching.

Vitamin C

Vitamin C is also water-soluble and is generally safe for animals. Toxicity is rare, but it can cause mild stomach upset if taken by mouth and only rarely leads to more serious symptoms.

Vitamin D

Vitamin D comes in two forms: ergocalciferol (D2) and cholecalciferol (D3). Toxicity is most often linked to cholecalciferol, since D2 is changed into D3 in the body. Toxic effects can happen at doses around 0.5 mg/kg or about 20,000 IU/kg of D3. High-dose vitamin D supplements made for people can be especially dangerous for pets. Signs of vitamin D poisoning in animals include vomiting, diarrhea, loss of appetite, belly pain, depression, and increased thirst and urination within the first day. More serious problems, such as kidney injury, high calcium levels, internal bleeding, or death, can develop within 24 to 48 hours after ingestion.

Vitamin E

Vitamin E alone rarely causes toxicity in animals and is usually well tolerated. Taking too much may cause mild stomach upset or gas. However, vitamin E can affect vitamin K-dependent clotting factors, which may increase the risk of bleeding, especially in animals taking anticoagulants like anti-Xa agents (such as apixaban or rivaroxaban) or vitamin K antagonists (such as warfarin).

Iron

As with people, animals can develop stomach upset from normal doses of iron supplements and too much can harm the liver. Toxicity has been seen at 20 mg/kg and happens in stages. In the first six hours, symptoms can include vomiting, diarrhea (sometimes with blood), belly pain, tiredness, and loss of appetite, followed by a short period of apparent recovery. More serious signs like shock, fast heart rate, tremors, jaundice, and heart failure can appear within 12 to 36 hours, and in severe cases, death can occur. Weeks later, survivors might have problems like internal bleeding, liver and kidney damage, or scarring in the intestines that causes blockages.

Magnesium

Magnesium poisoning is rare but can occur if an animal eats supplements, antacids, or laxatives that contain magnesium. Symptoms usually start 2 to 3 hours after ingestion and include stomach upset, slow heart rate, weakness, low calcium, and low potassium. Symptoms last 12 to 48 hours, or longer in animals with kidney problems.

Zinc

Zinc usually does not cause toxicity after a single large dose. However, if zinc levels in the blood stay high for a long time, it can lead to the breakdown of red blood cells, jaundice, pancreatitis, and sudden kidney injury, which may show as blood in the urine. If the poisoning is severe, a blood transfusion may be needed to treat anemia.

Probiotics

Probiotic supplements are being used more often to support digestive health in both people and animals. While human probiotics may not harm the pet, it is better to use probiotics made for animals because they are designed for the unique bacterial biome of each species.

Additives and Additional Ingredients

Vitamins and supplements are usually given for their main active ingredient, but manufacturers sometimes add other substances that can be dangerous for animals. The ingredients listed below can affect the nervous system, heart, and digestive tract, and using them together can make symptoms worse.

  • 5 hydroxytryptophan (5 HTP)
  • Caffeine (guarana, green tea)
  • Citrus aurantium (synephrine)
  • Ephedra (ma huang)
  • Fluoride
  • Yohimbine
  • Xylitol (birch sugar, wood sugar)

Although vitamins and supplements may benefit animal health, human products are not always safe for pets due to potentially inappropriate dosages and harmful excipients. Veterinary professionals should ad­ise clients that supplements intended for human use should never be administered to animals without veterinary guidance.

As a precaution, provide clients with the ASPCA Animal Poison Control Center hotline number at (888) 426-4435 for use in the event of accidental exposure.

References

By Denisa Colbrook, fourth-year pharmacy student, University of Illinois-Chicago

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