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
At the highest dose, the drug showed 76% efficacy —surpassing the 60% threshold for herd immunity.
—Noelle Harff, San Diego Union-Tribune, 31 Dec. 2025
While ongoing trials may clarify differences in efficacy and safety, Jirapinyo (who consults for Fractyl) expects operational features such as ease of use and procedure time to play a decisive role in determining uptake among practitioners.
—Elie Dolgin, IEEE Spectrum, 29 Dec. 2025
The decision was not tied to safety concerns or lack of efficacy, but to a broader shift in research priorities.
—New Atlas, 29 Dec. 2025
The infatuation spawned after beauty moguls Kylie Jenner, Hailey Bieber and Mikayla Nogueira touted the efficacy of Medicube’s PDRN products, including its Pink Peptide Serum and Pink Collagen Capsule Cream at the top of the year.
—Kaleigh Werner, Footwear News, 26 Dec. 2025
See All Example Sentences for efficacy
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Noelle Harff, San Diego Union-Tribune, 31 Dec. 2025
While ongoing trials may clarify differences in efficacy and safety, Jirapinyo (who consults for Fractyl) expects operational features such as ease of use and procedure time to play a decisive role in determining uptake among practitioners.
—Elie Dolgin, IEEE Spectrum, 29 Dec. 2025
The decision was not tied to safety concerns or lack of efficacy, but to a broader shift in research priorities.
—New Atlas, 29 Dec. 2025
The infatuation spawned after beauty moguls Kylie Jenner, Hailey Bieber and Mikayla Nogueira touted the efficacy of Medicube’s PDRN products, including its Pink Peptide Serum and Pink Collagen Capsule Cream at the top of the year.
—Kaleigh Werner, Footwear News, 26 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 6 Jan. 2026.
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