Synonyms
Examples of efficacy in a Sentence
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
Amber Smith, Discover Magazine, 6 Apr. 2024
Since the drug is still being researched, that means all the data on its safety and efficacy isn’t in yet.
—Syeda Khaula Saad, Verywell Health, 2 Apr. 2024
See all Example Sentences for efficacy 
These examples are programmatically compiled from various online sources to illustrate current usage of the word 'efficacy.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Word History
borrowed from Latin efficācia, from efficāc-, efficāx "capable of fulfilling a function, efficacious" + -ia -y entry 2
13th century, in the meaning defined above
Dictionary Entries Near efficacy
Cite this Entry
“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 16 Apr. 2024.
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More from Merriam-Webster on efficacy
Nglish: Translation of efficacy for Spanish Speakers
Britannica English: Translation of efficacy for Arabic Speakers
Britannica.com: Encyclopedia article about efficacy
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