synergisme

Synergism, or synergisme, is the phenomenon where the combined effect of two or more agents exceeds the sum of their separate effects. The term comes from Greek synergos, meaning “working together.”

In pharmacology and toxicology, synergism describes interactions that increase efficacy or toxicity beyond what would be expected from the individual agents. An additive effect equals the sum of separate effects; synergistic means greater than additive, while antagonistic means the combined effect is less. The concept is important for understanding drug combinations, chemical exposures, and risk assessment.

Common methods to assess synergy include the fractional inhibitory concentration (FIC) index and isobolographic analysis for drugs, as well as Bliss independence models. A classic medical example is the synergy between beta-lactam antibiotics and aminoglycosides, where one drug enhances uptake and the other provides bactericidal action, yielding a stronger effect than either drug alone.

Synergism also appears outside medicine. In ecology, multiple stressors such as drought and heat can produce disproportionately large impacts on populations or ecosystems. In chemistry and catalysis, cooperating catalysts or reaction partners can lower activation barriers more effectively together than separately, a phenomenon known as synergistic catalysis. Across disciplines, distinguishing true synergy from simple additivity requires careful experimental design and context-specific interpretation.