Photodegradation of ketoprofen (KET) generates radicals. It initiates chain oxidative reactions, leading to severe inflammatory conditions such as photosensitivity. Generally, antioxidants eliminate radicals generated in the body; however, incomplete elimination results in adverse side effects, such as oxidative stress. Previous studies have shown that local anesthetics inhibit KET photodegradation. However, local anesthetics do not exhibit radical-scavenging activity. Investigating the differences in the antioxidant activities of radical scavengers and local anesthetics through comparative analysis is crucial for identifying novel antioxidants that can replace traditional radical scavengers. Based on the characteristics of their antioxidant mechanism, radical scavengers can be classified into those targeting protein oxidation and those acting on lipid peroxidation. Focusing on the effects of lipid peroxidation, the relationship between local anesthetics and radical scavengers has been investigated. Similar to their protective effects against KET photodegradation, lidocaine (LDC) and dibucaine (DBC) inhibited the progression of lipid peroxidation reactions. This activity appears to be related to the structural flexibility of the LDC and DBC. Our findings suggest that LAs may inhibit lipid peroxidation by altering the orderliness of lipid membranes, which will be a new lipid-antioxidant approach.