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Folic Acid for Dogs, Cats, and Horses

By Barbara Forney, VMD

Last reviewed: 7/13/2022

Commonly prescribed for: Animals at Risk for Folate Deficiency

Species: Dogs, Cats, and Horses

Therapeutic Class: Water-soluble Synthetic Folate

Basic Information

Folic acid or vitamin B9 is a water-soluble synthetic folate. Naturally occurring folate is found in many foods. Folates have an important role in nucleoprotein synthesis, homocysteine metabolism, cellular division, erythropoeisis, neural development, and the synthesis of neurotransmitters. Folic acid is absorbed primarily by carrier-mediated diffusion within the proximal small intestine. Folic acid supplementation frequently is prescribed in humans during pregnancy and when animals or humans are taking drugs that may interfere with folate absorption. There are multiple drugs that may affect folate levels due to competitive, reversible inhibition of the enzyme dihydrofolate reductase.

Dogs and Cats

Folic acid supplementation is used in animals at risk for folate deficiency, particularly animals with small-intestinal disease or malabsorption. Serum folate levels should be determined prior to therapy; in some instances serum folate levels actually are increased due to bacterial synthesis of folate within the small intestine. Cats with exocrine pancreatic insufficiency are more likely to have folate deficiency than dogs with pancreatic insufficiency because of the synthesis of folate by small intestinal bacteria in dogs.

Research on cleft palates in brachycephalic breeds of dogs supports the use of folic acid supplementation in the pregnant bitch as a means of decreasing the incidence of cleft palate by as much as 48 - 76%. There is a great deal of research supporting folic acid supplementation in pregnant women as a means of preventing neural-tube defects.

Hyper homocysteinemia is a risk factor for thromboembolism in people; there is some preliminary data that supports the use of folic acid supplementation in cats with hyper homocysteinemia or those recovering from thromboembolism.


Folic acid supplementation sometimes is used in horses, particularly broodmares and breeding stallions, undergoing long-term treatment for equine protozoal myeloencephalitis with the anitprotozoal drugs pyrimethamine and sulfonamides. These drugs are known to inhibit dihydrofolate reductase.

Folic Acid Side Effects

Folic acid is considered relatively nontoxic; side effects are unlikely. CNS side effects have occurred in humans following very high doses.


Folate levels may be variable in dogs with enteropathy. Before administering supplemental folic acid, cobalamin and folate levels should be established.

Drug Interactions

  • Drugs that interfere with folate utilization include anti-convulsants (dilantin, phenytoin and primidone), sulfasalazine, barbiturates, nitrofurantoin, methotrexate, trimethoprim and pyrimethamine.
  • Chloramphenicol may slow the response to folic acid supplementation.


In cases of accidental overdose, excess folic acid will be metabolized or excreted in the urine.
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