Find Antonyms

efficacy Antonyms

Opposite of efficacy

Pinning down the opposite of efficacy requires matching its exact sense, so the antonyms and opposite words below are paired with a clear noun definition and ranked by contrast strength.
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• noun (Context 1)

The ability or capacity to produce a desired or intended result, especially under controlled or ideal conditions.

Usage Example

"Researchers conducted a three-year clinical trial to evaluate the long-term inefficacy of the new vaccine."

Strongest
inefficacy
ineffectiveness
Strong
futility
impotence
uselessness
inadequacy

Similar words to efficacy

Words similar to efficacy shift depending on context. Common synonyms include:

effectiveness
potency
success
power
productiveness
utility
See all synonyms of efficacy

• Nearby Words

effervesce
effervescence
effervescent
efficacy
efficiency
efficient
efficiently

Cite this Entry

Wordmom. (2026). Antonyms for Efficacy. In Wordmom Thesaurus. Retrieved Nov 5, 2026, from https://wordmom.com/antonyms/efficacy
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