efficacy

American  

[ef-i-kuh-see] / ˈɛf ɪ kə si /

Sometimes efficacity

noun

plural

efficacies

1. the capacity for producing a desired result or effect.

   Short, frequent periods of practice were shown to have greater efficacy than longer and less frequent ones.

2. a measure of the success of a vaccine or other pharmaceutical when used in the controlled environment of a clinical trial, as opposed to in the real world.

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efficacy British  

/ ˈɛfɪkəsɪ /

noun

1. the quality of being successful in producing an intended result; effectiveness

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Other Word Forms

• nonefficacy
  noun

Etymology

Origin of efficacy

First recorded in 1520–30; from Latin efficācia, from efficāc- (stem of efficāx ) “effective, effectual” + -ia, noun suffix; see efficacious ( def. ), -y ³ ( def. )

Explanation

The degree to which a method or medicine brings about a specific result is its efficacy. You might not like to eat it, but you can't question the efficacy of broccoli as a health benefit. Efficacy is a more formal way to say effectiveness, both of which stem from the Latin verb efficere "to work out, accomplish." The effectiveness, or efficacy, of something is how well it works or brings the results you hoped for. A scientist does research to determine the efficacy of a vaccine or medicine under development. If it is efficacious, it will cure or prevent a disease.

Example Sentences

Efficacy measures the maximum response a ligand can elicit, and potency measures the amount of ligand required to elicit half of the maximum response.

From Science Daily • Dec. 21, 2023

Efficacy is one, but other considerations include reusability, keeping the dead animals out of sight, and remote notification that a trap has been activated.

From New York Times • Feb. 27, 2023

Efficacy data in humans, however, are much more limited, making some researchers and regulatory agencies hesitant about authorizing tecovirimat’s widespread use.

From Scientific American • Aug. 26, 2022

Efficacy against severe to critical disease was 100%, although the number of COVID-19 cases observed was small—only eight in the placebo arm, and none in the vaccine arm.

From Science Magazine • Sep. 22, 2021

Besides all this, those Remedies from which the chief Efficacy and Operation against the Disease was expected, still remain’d secret with the Physicians, who thought it no Trouble to prepare them with their own Hands.

From Medicina Flagellata Or, The Doctor Scarify'd by Anonymous

Related Words

• adequacy
• competence
• effectiveness
• potency
• virtue