EFFICACY Synonyms: 22 Similar and Opposite Words

efficacy

noun

ˈe-fi-kə-sē

Definition of efficacy

as in effectiveness

the power to produce a desired result questioned the efficacy of the alarms in actually preventing auto theft

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Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of efficacy Kennedy has a history of casting doubts on vaccines and spreading misleading claims about their safety and efficacy. — Stephanie Stahl, CBS News, 27 Aug. 2026 Without needing to establish safety or efficacy, researchers can skip ahead to trials testing their broader potential. — Mike McRae 26, New Atlas, 26 Aug. 2026 But over time, people’s loyalty to online brands may be supplanted by the efficacy of their interfaces for agents. — George C. Lee Ii, Fortune, 26 Aug. 2026 Ongoing trials, for example, are studying the efficacy of B7-H3 as a target for antibody-drug conjugates, a cancer treatment in which antibodies bind to proteins on cancer cells to more directly deliver chemotherapy drugs. — Isabella Backman, Hartford Courant, 24 Aug. 2026 See All Example Sentences for efficacy

Recent Examples of Synonyms for efficacy

Noun

Calcium and vitamin D are often supplemented together for bone health, but research shows mixed results on their effectiveness in improving bone mineral density or reducing fracture risk.

— Jennifer Lefton, Verywell Health, 3 Sep. 2026
Milwaukee police officials have stood by the technology's effectiveness, despite months of criticism and two officers facing criminal charges for misuse of the system.

— David Clarey, jsonline.com, 3 Sep. 2026

Definition of effectiveness

Noun

That aircraft will put the Z4’s unusual airframe through its first full-scale flight test, bringing JetZero one step closer to finding out whether its efficiency targets can work beyond the drawing board.

— Aamir Khollam, Interesting Engineering, 31 Aug. 2026
Sharing components and collaborating on research will help cut costs and speed up development, as well as add efficiency in economy of scale once the vehicles go into production.

— ABC News, ABC News, 31 Aug. 2026

Definition of efficiency

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efficacity

efficacy

efficiency

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“Efficacy.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/efficacy. Accessed 4 Sep. 2026.

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Synonyms of efficacy

noun

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