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 once-daily, oral medication is proven to reduce the frequency and intensity of hot flashes and night sweats, based on clinical studies measuring efficacy at 4 and 12 weeks.
—Marnie Goodfriend, Flow Space, 29 Oct. 2025
If there were, there’d be safety in numbers and a sense of efficacy.
—Michael Shank, MSNBC Newsweek, 27 Oct. 2025
Issue clear, accessible guidance to pharmacists, health care providers, and to the public about the safety and efficacy of COVID-19 vaccines.
—Jenna Prestininzi, Freep.com, 27 Oct. 2025
But for a team that has had such drastic swings in five-on-five efficacy, Detroit is going to need to rely on consistent contributions from the power play.
—Max Bultman, New York Times, 26 Oct. 2025
See All Example Sentences for efficacy
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.
Marnie Goodfriend, Flow Space, 29 Oct. 2025
If there were, there’d be safety in numbers and a sense of efficacy.
—Michael Shank, MSNBC Newsweek, 27 Oct. 2025
Issue clear, accessible guidance to pharmacists, health care providers, and to the public about the safety and efficacy of COVID-19 vaccines.
—Jenna Prestininzi, Freep.com, 27 Oct. 2025
But for a team that has had such drastic swings in five-on-five efficacy, Detroit is going to need to rely on consistent contributions from the power play.
—Max Bultman, New York Times, 26 Oct. 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 5 Nov. 2025.
Copy CitationKids Definition
Love words? Need even more definitions?
Merriam-Webster unabridged
Share