efficacious

[ ef-i-key-shuhs ]

adjective

1. capable of having the desired result or effect; effective as a means, measure, remedy, etc.:

   The medicine is efficacious in stopping a cough.

efficacious

/ ˌɛfɪˈkeɪʃəs /

adjective

1. capable of or successful in producing an intended result; effective as a means, remedy, etc

Derived Forms

• ˌeffiˈcaciousness, noun
• ˌeffiˈcaciously, adverb

Other Words From

• effi·cacious·ly adverb
• effi·cacious·ness noun
• nonef·fi·cacious adjective
• nonef·fi·cacious·ly adverb
• unef·fi·cacious adjective
• unef·fi·cacious·ly adverb

Word History and Origins

Origin of efficacious¹

First recorded in 1520–30; from Latin efficāci- (stem of efficax ) “effectual.” See efficient, -acious

Word History and Origins

Origin of efficacious¹

C16: from Latin efficāx powerful, efficient, from efficere to achieve; see effect

Example Sentences

In a paper published in Molecular Psychiatry, researchers outline a new framework for understanding how antidepressants are efficacious in treating MDD.

From Science Daily

“If something was to be made available and shown to be efficacious and safe, I think there would be wide use of it,” Jonker says.

From Science Magazine

The low dose was a little more than 65% efficacious in both cases.

From Science Magazine

The authors note that gadolinium has not been tested in humans and has not been deemed to be safe or efficacious.

From Science Daily

Figuring out which drugs to stop temporarily requires further consultations while the time for efficacious use of Paxlovid dwindles, he said.

From Salon

When To Use

What are other ways to say efficacious?

The adjective efficacious describes things that are capable of having the desired result or effect. But efficacious isn’t quite the same as effectual, effective, or efficient! Find out why on Thesaurus.com.