O-Desmethylnaproxen is an active metabolite of naproxen, a widely used nonsteroidal anti-inflammatory drug (NSAID). It contributes significantly to the overall pharmacological effect of naproxen by inhibiting cyclooxygenase (COX) enzymes, particularly COX-1 and COX-2, which are involved in the production of prostaglandins that mediate pain, inflammation, and fever. Due to its anti-inflammatory, analgesic, and antipyretic properties, O-Desmethylnaproxen plays a key role in managing conditions such as osteoarthritis, rheumatoid arthritis, and other musculoskeletal disorders. Its presence in the bloodstream prolongs the therapeutic action of naproxen, enhancing the drug’s duration of effect. Additionally, because it is formed in the liver through metabolic processes, individual variations in metabolism can influence the efficacy and safety profile of naproxen therapy. Monitoring levels of this metabolite may help in understanding patient-specific responses and optimizing dosing strategies in chronic pain management.