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.
More than 100 scientific studies have been conducted to examine the safety and efficacy of using mifepristone and misoprostol to end a pregnancy. Alejandra O’Connell-Domenech, The Hill, 19 May 2025 The close call, however, prompted Congress to require more rigorous safety and efficacy data from drug manufacturers and empower the FDA to monitor the industry more closely. David Armstrong, CNN Money, 10 May 2025 Pharmaceutical companies have agreed to pay Hawaii $700 million to settle its lawsuit over the efficacy and safety of the blood thinner Plavix, the state attorney general's office announced Friday. CBS News, 10 May 2025 Furthermore, in light of the study’s findings, the Financial Accounting Standards Board will want to carefully monitor the efficacy of the new tax disclosures in their post-implementation review to mitigate concerns associated with companies lowering the quality of their tax disclosures. Nathan Goldman, Forbes.com, 9 May 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 25 May. 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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