Aspirin is a popular painkiller and anti-clotting agent used widely around the world. It is an NSAID derived from salicin, a naturally-occuring substance which can be found in many plants and trees.

Despite how safe it is for people, it is not usually recommended for use in dogs due to the risk of bleeding, with NSAIDs created especially for pets (e.g. Rimadyl®) being the more popular choice for treating pain and inflammation, particularly if long-term treatment is needed.

If you do use this medicine make sure your formulation does not contain any extra active ingredients such as acetaminophen which can be toxic to dogs. You should also be sure to discuss whether your dog is suitable for treatment with your vet before using the medicine.

Important Warning:

The problem with aspirin is that it raises levels of salicylate in the blood and can cause life-threatening side effects in dogs including internal bleeding and kidney damage.

To treat your dog’s pain without the dangerous side effects of aspirin, we recommend the following natural alternatives:

Flexpet – A safe, natural and clinically-proven remedy for arthritis and joint pain in dogs. Works to stop pain in just 7 days!

Promaxol – An all-natural remedy specially created to relieve general symptoms of pain in dogs.

Recommended Dosage

Note: This medicine can cause internal bleeding and other nasty side effects regardless of coating, always speak to your vet before giving it to your dog. It’s better to try natural supplements such first to avoid the potential risks of aspirin.

The usual dosage when treating healthy dogs is 5 mg/lb given by mouth twice daily (at most), though dogs with medical conditions such as hypoalbuminemia will often be given a lower dose or a different medicine.

If you’re using a human formulation you can use either “baby-strength” (81 mg) or regular strength pills (325 mg) depending on the size of your dog. However, veterinary formulations are generally better and come in strengths which are easier to work with.

Chart displaying the common canine dosage of aspirin
Dog’s Weight In Pounds: Dosage In Mg:

It’s also important to know the difference between the most common types of aspirin as some of them can be harmful or ineffective:


Plain (or uncoated) aspirin is intended for human use. In dogs uncoated formulations could irritate the lining of the stomach and cause internal bleeding.


This formulation is made to protect the stomach from the effects of the drug. However it is not effective for treating dogs as they do not always digest the coating fully, meaning enteric-coated formulations will not always be able to provide enough relief from pain. Studies have also failed to show any real difference between the effects of enteric-coated and uncoated formulations on the stomach.


Buffered medicines contain ingredients to balance the drug’s acidity which in theory helps to protect the stomach, though studies have shown that even buffered aspirin can cause bleeding and irritation. If you must use aspirin to treat your dog this is the type you should use. Most formulations created for animals will be buffered but it’s always a good idea to double check.

Dosage Example: A 65 lb dog would require 325 mg, which is equal to one regular strength human pill. For a table showing rough estimates of the amount of tablets your dog will need, see this page.

How Safe Is It?

While not as commonly used as veterinary painkillers like Metacam® and Rimadyl®, it can provide pain relief in a pinch. The majority of possible complications are related to stomach irritation and bleeding, but you can help to minimize this risk by administering the medicine with food and only using it on rare occassions.

It may not be suitable for animals suffering with:

  • Internal ulcers or bleeding
  • Problems with the blood or clotting
  • Von Willebrand’s Disease
  • Liver or kidney disease
  • Vitamin K deficiency

It can be used in dogs with hypoalbuminemia, but a lower dosage may be needed to prevent toxicity.

It should not be given to pregnant or nursing dogs or to puppies who do not yet have the correct digestive enzymes to process the drug. It may also delay labor.

Important: This drug stops blood from clotting properly making it especially dangerous when given to those with internal bleeding or peptic (stomach) ulcers.

Safety Guidelines

When treating a dog with this medicine we recommend that you:

  • Tell your vet about any of the dog’s existing medical conditions

  • Tell the vet about any other supplements or medicines your pet is taking

  • Tell the vet about any bad reactions your dog has had to NSAIDs in the past

  • Always use the “buffered” form to help prevent damage to the stomach

  • Give the medicine with food to further protect from stomach damage

Dangerous effects can occur when aspirin is given with other medicines that raise serum salicylate levels (such as Pepto-Bismol) or with other drugs that thin the blood (such as warfarin).


Toxicity begins at around 30 mg/lb. Levels this high can cause severe kidney damage and extreme blood loss which could quickly become life threatening. You can find some of the most common overdose symptoms near the bottom of this page.

What Can It Be Used For?

Aspirin is used all over the world as a painkiller. When given to dogs it may be used to treat the following:

  • Pain
  • Fever
  • Inflammation
  • Arthritis
  • Swelling
  • Glomerular disease

It can also have a positive effect on the heart. Despite its contraindication for dogs with kidney disease, aspirin has been used the past to treat glomerular disease.

Aspirin is a poor choice for the long-term management of arthritis as there’s some evidence to show that it could harm the joints and cartilage when used on a regular basis.

Possible Side Effects


Avoid giving aspirin to your dog if he has stomach ulcers, due to the heightened risk of internal bleeding.

During your pet’s treatment the following adverse effects are possible:


  • Vomiting
  • Diarrhea
  • Bleeding

Less Common

  • Internal bleeding *
  • Stomach ulcers
  • Intestinal ulcers


  • Organ damage

* Look out for dark, tarry stools or traces of blood in urine which can indicate this problem. If you suspect internal bleeding call the vet immediately and stop using the medicine.

Be on the lookout for some the “stealthier” symptoms of a bad reaction. Vomiting coupled with changes in levels of thirst could be a sign of kidney damage. Kidney damage most often occurs in pets with existing kidney problems, and is thought to be a result of a reduction in the blood supply to the kidneys.

Over time the damaging gastric effects of aspirin can reduce. This may be due to the way the drug works, by producing a substance known as ATL (aspirin-triggered lipoxin) which has a protective effect on the mucous membranes of the stomach. However, aspirin is only recommended for use in the short term, for a longer-term solution, seek other medications.

Overdose Symptoms:

An overdose could be fatal if left untreated. If you suspect you have accidentally overdosed your pet (anything at or above 30 mg/lb is toxic) or if they have eaten a large/unknown number of tablets you should call a vet right away. Symptoms of overdose can include:

  • Loss of appetite (early sign)
  • Vomiting and diarrhea
  • Extreme loss of blood
  • Internal hemorrhage
  • Internal ulcers
  • Weakness
  • Collapse


Dr. D. Lascelles
Plumb’s Veterinary Drug Handbook (sixth edition)