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
Metcalfe Park community leaders and residents see the resolution as a step in the right direction but question its efficacy.
—April Quevedo, jsonline.com, 7 Nov. 2025
The data shows eloralintide offers the potential for strong efficacy with improved tolerability and could serve as an alternative to incretin therapies, said Kenneth Custer, president of Lilly Cardiometabolic Health.
—Reuters, NBC news, 6 Nov. 2025
However, by the time of the American withdrawal from Afghanistan in 2021, which allowed the Taliban to return to power, the perception of the morality and efficacy of that long war had dwindled in the international community.
—Literary Hub, 5 Nov. 2025
However, Weng said these challenges and growth barriers also make ongoing research to improve the safety and efficacy of robots even more important.
—Prabhat Ranjan Mishra, Interesting Engineering, 5 Nov. 2025
See All Example Sentences for efficacy
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April Quevedo, jsonline.com, 7 Nov. 2025
The data shows eloralintide offers the potential for strong efficacy with improved tolerability and could serve as an alternative to incretin therapies, said Kenneth Custer, president of Lilly Cardiometabolic Health.
—Reuters, NBC news, 6 Nov. 2025
However, by the time of the American withdrawal from Afghanistan in 2021, which allowed the Taliban to return to power, the perception of the morality and efficacy of that long war had dwindled in the international community.
—Literary Hub, 5 Nov. 2025
However, Weng said these challenges and growth barriers also make ongoing research to improve the safety and efficacy of robots even more important.
—Prabhat Ranjan Mishra, Interesting Engineering, 5 Nov. 2025
See All Example Sentences for efficacy
Cite this Entry
“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 15 Nov. 2025.
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