Which term describes two drugs that decrease each other's effectiveness?

• A. Synergism
• B. Therapeutic Effect
• C. Antagonism
• D. Adverse drug effect

Answer: (C)

Antagonism happens when two drugs oppose each other’s actions and end up reducing the overall effect of one or both drugs. This can occur if one drug blocks receptor sites that another drug needs, if they compete for the same receptors, or if one drug speeds up the metabolism and lowers the concentration of the other. A classic example is a medication that blocks opioid receptors, which diminishes the effect of an opioid taken at the same time. This is different from synergism, where drugs boost each other’s effects, therapeutic effect which is the beneficial outcome, and adverse drug effects which are unwanted side effects.