How do aspirin and ibuprofen reduce pain related to inflammation?

Aspirin and ibuprofen reduce pain related to inflammation by inhibiting the synthesis of prostaglandins.12

Prostaglandins are lipid compounds that act as chemical messengers and are key mediators of the inflammatory response. When tissues are injured, the enzyme cyclooxygenase (COX) facilitates the conversion of arachidonic acid into prostaglandins. These substances induce local tissue responses—including pain, swelling, heat, and redness—by dilating blood vessels and increasing their permeability, which allows white blood cells to enter the affected area.32

By acting as COX inhibitors, aspirin and ibuprofen block the production of these prostaglandins. This suppression of prostaglandin synthesis reduces the sensitization of peripheral nerve fibers that report noxious events, thereby alleviating the pain and inflammation associated with conditions like rheumatoid arthritis. While effective, it is important to note that because prostaglandins also serve protective functions in the body, such as maintaining the stomach lining, these drugs can sometimes cause side effects like peptic ulcers.234