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
Liam Neeson is denying being part of the anti-vaccine movement, after lending his voice to a documentary that questions the efficacy of the medical advance.
—Anna Kaufman, USA Today, 12 Dec. 2025
However, there haven't been any meaningful studies studies that prove these treatments’ efficacy.
—Kelsey Lentz, PEOPLE, 12 Dec. 2025
Pfizer pointed to previous statements supporting the safety and efficacy of its Covid vaccine.
—Annika Kim Constantino, CNBC, 12 Dec. 2025
Reed's latest attack and arrest have raised questions about the efficacy of electronic monitoring.
—Sara Tenenbaum, CBS News, 10 Dec. 2025
See All Example Sentences for efficacy
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Anna Kaufman, USA Today, 12 Dec. 2025
However, there haven't been any meaningful studies studies that prove these treatments’ efficacy.
—Kelsey Lentz, PEOPLE, 12 Dec. 2025
Pfizer pointed to previous statements supporting the safety and efficacy of its Covid vaccine.
—Annika Kim Constantino, CNBC, 12 Dec. 2025
Reed's latest attack and arrest have raised questions about the efficacy of electronic monitoring.
—Sara Tenenbaum, CBS News, 10 Dec. 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 Dec. 2025.
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