Metformin for dogs: Uses and safety

In this article:

• What is metformin used for in dogs?
• Is metformin safe for dogs?
• Dosage
• Alternatives

In this article

• What is metformin used for in dogs?
• Is metformin safe for dogs?
• Dosage
• Alternatives

Metformin is not commonly used in veterinary medicine. Though sometimes used in cats and birds, there are no veterinary guidelines for its use in dogs. 

In medicine, metformin is used to lower blood glucose levels in people with Type 2 diabetes mellitus. In dogs, the standard treatment for diabetes is insulin. Veterinarians don’t use oral antidiabetic drugs like metformin in dogs. However, there is limited research suggesting metformin may slow down the progress of heart failure in dogs, so that’s one possible veterinary use of metformin in the future.

What is metformin used for in dogs?

Veterinarians do not use metformin in dogs. Doctors use metformin as a first-line drug to reduce blood sugar levels in people with Type 2 diabetes. Veterinarians treat canine diabetes—both Type 1 and Type 2 diabetes—almost exclusively with insulin. They do not use oral antihyperglycemic medications like metformin.

Metformin’s mechanism of action is unique among antidiabetic drugs. It increases insulin sensitivity by activating an enzyme in the body’s tissues that regulates certain metabolic processes, including glucose uptake. In this way, the body’s cells increase their uptake of blood sugar. It’s a good starter drug for people with insulin resistance. It’s effective and has relatively few side effects. Most importantly, people taking metformin are less likely to experience low blood sugar or lactic acidosis, the most concerning problems associated with antihyperglycemic drugs.

Metformin is less useful at treating diabetes in small animals. However, research has shown that metformin may help extend the lives of dogs with heart failure, so that’s one possible use. 

There is research and recommended dosages on using metformin in cats with Type 2 diabetes (also called noninsulin-dependent diabetes mellitus or NIDDM). The use of metformin in cats is controversial, so veterinarians are more likely to use proven, FDA-approved medications like Bexacat (bexagliflozin) or Senvelgo (velagliflozin) in diabetic cats.

Veterinarians are free to prescribe human medications to dogs, but a veterinarian will have no clinical research or standardized dosages to help guide treatment metformin treatment in a dog.

Is metformin safe for dogs?

Metformin is not used in dogs but has been used in research studies. It did not raise any concerns with safety in the research, but it hasn’t been proven to be safe for clinical use.

If a dog accidentally ingests metformin, call an emergency veterinary hospital for advice. 

Side effects of metformin in dogs

The only reported side effects are those that occur when dogs accidentally eat metformin intended for people. In nearly every case, the dogs experienced vomiting, so the most common side effect of metformin in dogs is:

• Vomiting

Other side effects reported in dogs who have ingested metformin pills are:

• Lethargy
• Diarrhea
• Lowered body temperature
• Low blood pressure
• Pale gums and mouth tissues
• Tremors

Caregivers should call the ASPCA Animal Poison Control Center or an emergency animal hospital if the dog has swallowed metformin or shows any clinical signs of a metformin overdose.

Serious adverse effects such as low blood sugar (hypoglycemia) and lactic acidosis are possible but rare.

Interactions of metformin with other pet meds

Veterinary researchers have not studied the drug interactions of metformin. Based on its use in people, metformin may cause problems in an animal when taken with:

• Blood pressure drugs called ACE inhibitors
• Thiazide diuretics or furosemide
• Corticosteroids

Metformin dosage for dogs

Veterinary medicine does not have standardized or recommended metformin dosages for dogs. If the drug is prescribed to a dog, it can only be purchased in formulations made for people.

Can dogs overdose on metformin?

Dogs can overdose on metformin. Most cases of metformin overdose are due to accidental ingestion. 

So far, there have been no reported fatalities in dogs that have overdosed on metformin. Reported cases of severe low blood sugar and lactic acidosis are rare. 

That doesn’t mean an overdose is to be taken lightly. When a dog has ingested metformin, caregivers should immediately call the ASPCA Animal Poison Control Center or a veterinary emergency hospital for advice on what to do next.

The most common and nearly universal symptom of a metformin overdose in a dog is vomiting, though the dog may show other gastrointestinal signs like distress or nausea. Other clinical signs of a metformin overdose include hypothermia, low energy, diarrhea, hindquarter tremors, low blood pressure, and pale mucous membranes. 

Metformin alternatives for dogs

Metformin has two possible uses in dogs.

In people, metformin is used to treat Type 2 diabetes. It is a biguanide oral diabetes drug that reduces blood sugar by increasing insulin sensitivity and reducing the liver’s production of glucose.

Oral antidiabetic medications are not used in dogs. The sole treatment is insulin for both Type 1 and Type 2 diabetes.

Limited research has shown that metformin slows the progress of heart failure in research dogs. That’s a possible use for metformin not only in animals but people, as well. The standard treatments for heart failure in dogs are ACE inhibitors to lower blood pressure, diuretics to reduce fluid buildup, and pimobendan to improve the heart’s performance. Metformin could be added to these drugs because it seems to have heart-protective properties.

Summary

Metformin is not used in dogs but it’s not prohibited, either. There is no research on its clinical use in dogs. There are no standard or recommended dosages for dogs, but there are recommended metformin dosages for cats and horses. The bottom line is that caregivers should not give their dogs metformin.