Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Iron deficiency in dogs and cats is almost always caused by chronic blood loss, such as heavy flea or hookworm infestations or bleeding in the stomach or intestines, not by diet. Pets on complete diets get enough iron. Iron supplements may be prescribed after the cause is found, but giving iron without testing can be harmful, and human iron pills are a common cause of poisoning in dogs.
Signs of anemia
- Pale gums
- Weakness or tiring easily
- Fast breathing or heart rate
- Black, tarry stool (possible gut bleeding)
Common causes of iron deficiency
- Heavy flea infestations, especially in puppies and kittens
- Hookworms
- Stomach or intestinal ulcers or tumors
- Other chronic bleeding
How vets treat it
- Find and stop the source of blood loss
- Parasite treatment
- Iron supplementation, by mouth or injection, as prescribed
- Blood transfusions for severe anemia
Iron poisoning
Human iron supplements and prenatal vitamins can cause vomiting, bloody diarrhea, and liver damage in pets. If your pet swallows iron pills, call your vet or ASPCA Animal Poison Control Center (888) 426-4435 or Pet Poison Helpline (855) 764-7661 (fees apply).
What to avoid
- Giving iron or multivitamins “for energy” without a diagnosis
- Human supplements
Sources
- Merck Veterinary Manual: Iron deficiency anemia
- Merck Veterinary Manual: Iron toxicosis
- Companion Animal Parasite Council (CAPC): Hookworms
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.