Which effect occurs when two drugs both influence an indicator in the same manner?

The additive effect describes a situation where two drugs with similar actions combine to produce an effect that is equal to the sum of their individual effects. When both drugs influence an indicator in the same manner, their combined effect can enhance the overall outcome, making it more significant than the effect of either drug alone. This concept is important in pharmacology and toxicology, as it helps in understanding how different substances can interact within the body and the potential for increased efficacy or heightened risk when multiple drugs are used simultaneously.

The other options represent different types of interactions: the antagonistic effect occurs when one drug counteracts the action of another, the null effect implies no significant effect from the combination, and the overlapping effect isn't a standard term in pharmacology but may suggest some degree of similarity without quantifying it. Understanding these interactions is crucial for safe drug administration and assessing potential hazards.