Chapter 3 examines the health effects-based interpretation of the principle prohibiting superfluous injury or unnecessary suffering (SIrUS) in the law of armed conflict (LOAC), highlighting a transition from solely military considerations to an emphasis on the long-term health consequences. This chapter examines the origins of this approach within the context of the two Additional Protocols of 1977 to the Geneva Conventions of 1949, which possibly enhanced protection by associating unnecessary suffering with health effects. This chapter analyzes endeavors such as the SIrUS Project and looks at the long-term health effects of chemical, biological, and nuclear weapons, illustrating how medical insights increasingly shape the interpretation of SIrUS. Thus, the following chapter examines the evolution toward the medicalization of the principle, highlighting how contemporary legal debates contest traditional interpretations and emphasize human health as a critical consideration in the legality of the use of weapons in contemporary warfare.