We give our 20-lb Pup one baby aspirin if she's had a rough day and her hips are aching. This is done upon the vet's recommendation.
However, I don't know if aspirin is safe in larger quantities?
Okay, I checked in my doggy First Aid book, and it says that "Never give your pets any unprescribed medication without consulting a vetrinarian. Over-the-counter medications for humans, such as ibuprofan and acetiminophen (Tylenol), are toxic to pets!"