what word describes how well a drug works?

The main word that describes how well a drug works is efficacy.

Core term: efficacy

• In medicine and pharmacology, efficacy means the ability of a drug or treatment to produce the desired therapeutic effect.

• More specifically, it often refers to the maximum effect a drug can achieve, regardless of the dose.

Related concept: effectiveness

• Another close term is effectiveness , which describes how well a drug works in real‑world, routine clinical use rather than in ideal clinical trial conditions.

• So, efficacy is “does it work under ideal conditions?”, while effectiveness is “does it work well in everyday practice?”.

TL;DR: If you are answering a question like “what word describes how well a drug works?”, the best single word is efficacy.

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