formal10K+

Efficacy

UK //ˈɛfɪkəsi//US //ˈɛfɪkəsi//

Definition

The ability of something to produce the desired result.

In simple words: Effectiveness or how well something works.

Examples

The efficacy of the new vaccine was confirmed in clinical trials.
Researchers are studying the efficacy of various treatment methods.
The efficacy of the policy was debated in the meeting.
Her confidence in the efficacy of the project motivated the team.
It is important to evaluate the efficacy before implementation.

Usage notes

Used primarily in formal contexts like research, medicine, and discussions about policy. Less common in everyday conversation.

Grammar pattern

standalone noun

Memory hint

Think 'effective' and 'capacity' together - the capacity to be effective.

Collocations

clinical efficacy
evaluate efficacy
prove efficacy
demonstrate efficacy
measure efficacy

Synonyms

effectiveness
potency
efficaciousness
success
utility

Common mistakes

Confused with 'efficiency', which refers to doing things quickly and without waste.
Often used without proper context; needs to specify what is being evaluated.
Mispronounced, especially by non-native speakers.