efficacy

noun

ef·​fi·​ca·​cy ˈe-fi-kə-sē How to pronounce efficacy (audio)
plural efficacies
: the power to produce an effect

Examples of efficacy in a Sentence

In the planner's view, Rumsfeld had two goals: to demonstrate the efficacy of precision bombing and to "do the war on the cheap." Seymour M. Hersh, New Yorker, 7 Apr. 2003
Vaccines exist, but their efficacy against aerosolized plague is unknown. Sharon Begley et al., Newsweek, 8 Oct. 2001
efficacy does not have to be demonstrated before homeopathic products are marketed. Alison Abbott et al., Nature, 26 Sept. 1996
questioned the efficacy of the alarms in actually preventing auto theft
Recent Examples on the Web
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.
They are often intertwined with political, moral and spiritual ideas around the rights of an individual versus the community, the limits of government power over bodily autonomy, mistrust of medical institutions and misinformation about shot safety and efficacy. Annika Kim Constantino, CNBC, 9 Mar. 2025 Like: Look for third-party certification seals on the label, which indicate the product has undergone an independent review of safety and efficacy; USP and NSF are popular ones. Dylan Scott, Vox, 7 Mar. 2025 The safety and efficacy of weight loss gummies are generally unknown, and no evidence supports taking them. Allison Herries, Verywell Health, 7 Mar. 2025 This includes ensuring that accurate information about vaccine safety and efficacy is disseminated. Angelica Stabile, Fox News, 7 Mar. 2025 See All Example Sentences for efficacy

Word History

Etymology

borrowed from Latin efficācia, from efficāc-, efficāx "capable of fulfilling a function, efficacious" + -ia -y entry 2

First Known Use

1527, in the meaning defined above

Time Traveler
The first known use of efficacy was in 1527

Browse Nearby Words

Cite this Entry

“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 12 Mar. 2025.

Kids Definition

efficacy

noun
ef·​fi·​ca·​cy ˈef-i-kə-sē How to pronounce efficacy (audio)
plural efficacies
: the power to produce a desired result

More from Merriam-Webster on efficacy

Last Updated: - Updated example sentences
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