See also:

Dog arthritis

Nutraceuticals for dog arthritis

Omega 3 supplements for dogs

Aspirin (dogs only)

Aspirin is ok for dogs, but not for cats. To reduce stomach irritation, use buffered aspirin or give aspirin at mealtime. For chronic arthritis pain, aspirin is a bad idea.  We have prescription drugs that are much safer and far more effective.  If your dog needs aspirin more often than once or twice a week you should change to something more effective.  

Use 5 grain (325 mg) aspirin tablets.

A 60 to 80 lb dog may be given one tablet twice a day (every 12 hours) or 1/2 tablet three times a day (every eight hours).  A 30 to 40 lb dog gets half as much; a 15 to 20 lb dog a quarter as much.