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
Freezing can also alter the physical properties of medications, leading to inconsistent dosing and reduced efficacy.
—Marina Johnson, Louisville Courier Journal, 5 Dec. 2025
Hughes also spoke to the efficacy of current USMCA rules of origin, cautioning the USTR against creating new restrictions.
—Kate Nishimura, Sourcing Journal, 4 Dec. 2025
Several presenters and panel members claimed there was limited evidence of the hepatitis B vaccine’s safety or efficacy, ignoring decades of evidence to the contrary.
—Erika Edwards, NBC news, 4 Dec. 2025
However, these are not generally recommended by health authorities due to a lack of evidence as to their efficacy and safety.
—Sashikala Vp, CNN Money, 4 Dec. 2025
See All Example Sentences for efficacy
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Marina Johnson, Louisville Courier Journal, 5 Dec. 2025
Hughes also spoke to the efficacy of current USMCA rules of origin, cautioning the USTR against creating new restrictions.
—Kate Nishimura, Sourcing Journal, 4 Dec. 2025
Several presenters and panel members claimed there was limited evidence of the hepatitis B vaccine’s safety or efficacy, ignoring decades of evidence to the contrary.
—Erika Edwards, NBC news, 4 Dec. 2025
However, these are not generally recommended by health authorities due to a lack of evidence as to their efficacy and safety.
—Sashikala Vp, CNN Money, 4 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 Dec. 2025.
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