Aspirin made for dogs is the same as that made for humans; you can purchase canine aspirin without prescription. Aspirin can treat pain or inflammation in dogs, but give it only after consulting with your vet. Some dogs don't tolerate aspirin well; they may react poorly to it or may become sick. Give aspirin only with food, and never give it to a dog long-term unless your vet instructs you otherwise.
Canine vs. Human
There is no medicinal difference between the aspirin manufactured and packaged for dogs to that made for humans, except for the dosage. Human aspirin is sold in dosages of 81 milligrams, 325 mg and 500 mg. Aspirin made for dogs comes in 120 mg and is sometimes flavored with beef or liver. The 120-mg dose may not be appropriate for some dogs. Veterinarians prefer newer analgesics such as rimadyl, firocoxib and meloxicam that are apparently more effective and safer for canines. These must be obtained from a vet.
What Aspirin Does
Dog aspirin is in a class of nonsteroidal anti-inflammatory drugs commonly known as NSAIDs. Aspirin helps to reduce the swelling and pain associated with joint or muscular pain from arthritis or injury. It is recommended for short-term use only, however. Using aspirin for an extended period may cause your dog to develop stomach ulcers or gastrointestinal upset. Your vet can prescribe a medication to protect your dog's stomach while he is taking aspirin, so consult her before using it.
Not All Alike
Certain types of aspirin are better for your dog. Aspirin made for dogs is either buffered or enteric. Buffered aspirin is preferable, because the enteric coating does not always break down in the dog's stomach, making it ineffective. These types of aspirin help to protect the dog's stomach from upset or ulcers. Neither dog nor human aspirin have been consistent in treating canine ailments, since dogs metabolize aspirin at difference rates. This makes its effectiveness unpredictable.
Canine aspirin can be toxic to dogs in high doses. Your vet can tell you how much to give your dog based on his weight and medical history. Your dog cannot take aspirin a week before surgery, during pregnancy or until he is full-grown. Symptoms of aspirin toxicity include loss of appetite, vomiting and diarrhea. These can cause internal bleeding in the small intestines or stomach. The dog may become weak or have difficulty walking. See your vet immediately if these symptoms occur.