efficacious
adjective
Did you know?
If you guesstimate that efficacious is the effect of combining effective with the suffix -ious, you’re on the right track. Efficacious came to English from the Middle French word efficace (or that word’s Latin source, efficāc- or efficāx), meaning “effective.” (These words ultimately trace back to the Latin verb efficere, “to make, bring about, produce, carry out.”) English speakers added -ious to effectively create the word we know today. Efficacious is one of many, er, eff words that mean “producing or capable of producing a result.” Among its synonyms are the familiar adjectives effective and efficient. Efficacious is more formal than either of these; it’s often encountered in medical writing where it describes treatments, therapies, and drugs that produce their desired and intended effects in patients.
Examples of efficacious in a Sentence
Kiana Murden, Vogue, 1 July 2025
Her medical training shaped how the brand formulates balancing potent actives with skin-soothing ingredients making sure the final product is efficacious without compromising the skin barrier.
—Meggen Harris, Forbes.com, 30 June 2025
Due to these higher costs, the incentive to invest in the next generation of medicines is diminished, reducing the odds that efficacious medicines for untreated conditions will be developed.
—Wayne Winegarden, Forbes.com, 28 May 2025
On the other side are patients living with untreated diseases hoping that pharmaceutical companies will soon develop an efficacious treatment.
—Wayne Winegarden, Forbes, 5 Mar. 2025
See All Example Sentences for efficacious
Cite this Entry
“Efficacious.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacious. Accessed 21 Jul. 2025.
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efficacious
adjective
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