Antibodies exert additive or synergistic effects with mechanisms of innate immunity. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Some drug interactions can be simplistically classified as either synergistic or inhibitory interactions. These effects are mediated by different mechanisms with synergistic action. A therapeutic index does not consider drug interactions or synergistic effects. Quinupristin and dalfopristin are protein synthesis inhibitors in a synergistic manner. This combination is synergistic in lowering blood pressure. Hormones can interact in permissive, synergistic, or antagonistic ways. Together these mechanisms lead to a synergistic interaction. The use of multiple-parasite antigens can therefore have a synergistic or additive effect. Mixtures of POPs can in principle produce synergistic effects. Pristinamycin is a mixture of two components that have a synergistic antibacterial action. And this is equally true of the synergistic effects produced by emergent systems. Two models predominate the field, which are synergistic and not mutually exclusive. Synergistic responses are a complicating factor in environmental modeling.