Antagonism is the opposite term to it.
A synergistic interaction is often of therapeutic interest, and measurement of synergy has been the topic of many researches. A quantitative value for the extent of synergy is important to optimize combination treatment. Methods to evaluate the interaction among agents with different IC50 values, but parallel concentration response curves are satisfactory. The inadequacy of existing methods and development of a new method will be discussed. It can be applied to combinations of agents with unparalleled shape of dose-response curve, where the classic approach will lose power.