Pain killers. View of a blister pack of pain killer pills with more pills spilling out of a bottle. The blister pack helps keep the pills separate and sterile. Most common pain killers (or analgesics) such as aspirin, work by preventing the formation of a pain signal within the nerves leading to the brain. Some analgesics, such as codeine, work by blocking the pain signal in the brain. Pain killers are taken to provide short-term relief from headaches, minor cuts and bruises, and rheumatic pain. Severe prolonged pain may be a sign of a more serious disorder, and medical advice should be sought.