Which term describes the ability of a drug to produce a specific effect?

The term that describes the ability of a drug to produce a specific effect is efficacy. Efficacy refers to the maximum potential therapeutic effect that a drug can achieve, meaning how well it works in producing the desired biological response when it binds to its target receptor. This is distinct from other pharmacological concepts such as potency, which indicates the amount of drug needed to produce a certain effect, and affinity, which refers to how strongly a drug binds to its receptor. Onset of action describes the time it takes for a drug to start having its effect after administration. Therefore, the correct answer reflects the drug's effectiveness in achieving its intended therapeutic goal.