Additive interactions occur when the combined effect of two or more substances or factors equals the sum of their individual effects. For example, if Drug A lowers blood pressure by 10 mmHg and Drug B lowers it by 5 mmHg, their combined effect would lower blood pressure by 15 mmHg. This type of interaction is straightforward and predictable. In contrast to synergistic interactions, where the combined effect is greater than the sum, additive interactions are simpler to understand and anticipate. They are commonly observed in pharmacology, environmental science, and various fields where multiple influences are at play, helping researchers and practitioners make informed decisions.