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Thiamine
What is thiamine?
Thiamine (Vitamin B1) is an injectable drug and oral vitamin supplement used for the prevention or treatment of thiamine deficiency. Pets may have increased dietary thiamine requirements due to nutritional deficiencies, malnutrition, burns, fever, gastrectomy, chronic hemodialysis, hepatobiliary disease, hyperthyroidism, prolonged infection, intestinal disease, long-term exertion, and prolonged stress. It is used for this purpose in many species, including dogs, cats, horses, cattle, small ruminants, and pigs.
Thiamine is also used in the treatment of cerebrocortical necrosis in cattle and sheep, in the adjunctive treatment of lead poisoning and ethylene glycol toxicity in cats and dogs, and as adjunctive therapy for seizures in dogs.
Thiamine injectable is only available by prescription from your veterinarian. Several generic veterinary formulations exist, as well as generic human formulations that may be used off-label in animal species. Many drugs are commonly prescribed for off-label use in veterinary medicine. “Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as their directions may be significantly different from those on the label.
The U.S. Food and Drug Administration (FDA) does not review non-drug health supplements (e.g., herbals, nutraceuticals, shampoos, and other supplements) for safety or effectiveness before they are sold to the public. Manufacturers of non-drug health supplements must ensure their supplements are safe and labeled accurately. The FDA requires that these non-pharmaceuticals contain a disclaimer that says, “This supplement is not intended to diagnose, treat, cure or prevent any disease.” Health Canada licenses “veterinary health supplements” after reviewing safety, efficacy, and manufacturing information provided by the manufacturer. These supplements are not tested by Health Canada.
Your veterinarian is the best source of information about the safety of non-drug health supplements in pets. Just because a supplement is natural does not mean it is safe. All medicines and medicinal plants are potentially toxic if used inappropriately or given at high doses. Supplements can also have side effects, like pharmaceuticals. Few supplements and herbs have been subjected to rigorous scientific trials to determine their efficacy.
Although the information in this handout may be helpful, it may also be incomplete and may not represent the full range of effects the supplement could have on your pet.
How do I give my pet thiamine?
Thiamine should take effect within several days, but improvements in clinical signs are not always outwardly noticeable. However, side effects can take effect immediately.
If you miss a dose, give it as soon as you remember. However, if it is almost time for the next scheduled dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.
Thiamine may cause the following side effects:
Serious adverse reactions associated with this supplement may occur without warning and could, in rare cases, lead to death. Anaphylactic reactions may occur after rapid or large IV injections. If any of the following signs develop, stop giving thiamine and contact your veterinarian immediately:
Sensitivities can develop over time with repeated exposure. Your pet may have no reaction after the first few doses but may develop a sensitivity later. It is important to watch for signs of an allergic reaction over the entire course of treatment.
Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This short-acting drug/supplement should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.
DO NOT USE thiamine in:
USE WITH EXTREME CAUTION in:
Contact your veterinarian if your animal's condition does not improve or worsens despite this treatment.
Certain medications should be used WITH CAUTION when given with thiamine, including:
Avoid raw fish, shellfish, bacteria, yeast, and fungi while taking this medication. These items contain high concentrations of enzymes called thiaminases, which degrade thiamine. Cooking destroys thiaminases.
Be sure to tell your veterinarian about any medications (including vitamins, supplements or herbal therapies) that your pet is taking before starting any treatment.
If you suspect an overdose or an adverse reaction to the supplement/treatment, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet's weight and symptoms. Report any adverse effects to the FDA or Health Canada.
© Copyright 2025 LifeLearn Inc. Used and/or modified with permission under license. This content written by LifeLearn Animal Health (LifeLearn Inc.) is licensed to this practice for the personal use of our clients. Any copying, printing or further distribution is prohibited without the express written consent of LifeLearn. This content does not contain all available information for any referenced medications and has not been reviewed by the FDA Center for Veterinary Medicine, or Health Canada Veterinary Drugs Directorate. This content may help answer commonly asked questions, but is not a substitute for medical advice, or a proper consultation and/or clinical examination of your pet by a veterinarian. Please contact your veterinarian if you have any questions or concerns about your pet’s health. Created on May 14, 2025.
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