efficacy
noun
ef·fi·ca·cy
ˈe-fi-kə-sē 
plural efficacies
: the power to produce a result or effect
increased teacher efficacy in classroom management
The efficacy of this treatment has not yet been proved.
In the upcoming … clinical trial, researchers will further investigate the efficacy and safety of the vaccine.—
Julia Landwehr
Julia LandwehrExamples 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
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
The Atlanta-area congressman was the fifth House member to die during the 119th Congress, and the fourth Democrat, amid an ongoing debate over lawmakers’ age and efficacy.
—Joseph Konig, PEOPLE, 30 Apr. 2026
Compared to skin care’s need to wait for efficacy validation, color cosmetics offer immediate gratification, lower decision-making costs, and even the promise of going viral online.
—Denni Hu, Footwear News, 29 Apr. 2026
Atomi noted that while supine movements are common in physical therapy and exercise programs such as Pilates, there’s been little scientific evidence of their efficacy.
—Lindsey Leake, NBC news, 29 Apr. 2026
This is critically important because most existing treatments for psychiatric conditions (including major depressive disorder and schizophrenia) involve a significant delay in efficacy.
—Eric J. Nestler, STAT, 28 Apr. 2026
See All Example Sentences for efficacy
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Joseph Konig, PEOPLE, 30 Apr. 2026
Compared to skin care’s need to wait for efficacy validation, color cosmetics offer immediate gratification, lower decision-making costs, and even the promise of going viral online.
—Denni Hu, Footwear News, 29 Apr. 2026
Atomi noted that while supine movements are common in physical therapy and exercise programs such as Pilates, there’s been little scientific evidence of their efficacy.
—Lindsey Leake, NBC news, 29 Apr. 2026
This is critically important because most existing treatments for psychiatric conditions (including major depressive disorder and schizophrenia) involve a significant delay in efficacy.
—Eric J. Nestler, STAT, 28 Apr. 2026
See All Example Sentences for efficacy
Cite this Entry
“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 3 May. 2026.
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