Most over the counter (OTC) pain medicine made for humans is poisonous for dogs. The only one that has been known to help dogs is aspirin (acetylsalicylic acid). A vet should be contacted first before giving aspirin to a dog.
Aspirin comes in many types. According to Mike Richards, DVM, enteric-coated aspirin should not be given to dogs because they cannot digest the coating.
"Dog Owner's Home Veterinary Handbook" (Debra M. Eldredge, DVM, et al.; 2007) recommends an aspirin dosage of 4 to 10 milligrams for every pound the dog weighs, given once or twice a day.
"The Pill Book Guide to Medication for Your Dog and Cat" (Kate A.W. Roby, VMD, et al.; 1998) recommends giving food with OTC aspirin to dogs because dogs taking it on an empty stomach often vomit it right back up.
Aspirin can cause a dog's blood to thin. Dogs undergoing surgery in one week or less should never be given aspirin.
Other OTC pain medicines like ibuprofen, naxoproxen or acetaminophen can kill a dog. If a dog eats these OTC drugs, contact a vet or the ASPCA Animal Poison Control Center immediately.