Analgesics are drugs used to relieve pain. There are many classes of painkillers. Demerol, morphine, codeine, and other narcotics are subject to federal regulation and cannot be purchased without a prescription.
Buffered or enteric-coated aspirin (acetylsalicylic acid) is an over-the-counter analgesic that is reasonably safe for a short time for home veterinary care in the recommended dosage for dogs. (Aspirin has a very low margin of safety for cats and should not be used.) Buffered or enteric-coated aspirin is much safer than regular aspirin because it is less likely to cause stomach and duodenal ulcers.