Antonyms of noun efficacy

1 sense of efficacy

Sense 1
efficacy, efficaciousness -- (capacity or power to produce a desired effect; "concern about the safety and efficacy of the vaccine")
       Antonym of inefficacy (Sense 1)
      => inefficacy, inefficaciousness -- (a lack of efficacy)

Synonyms/Hypernyms (Ordered by Estimated Frequency) of noun efficacy

1 sense of efficacy

Sense 1
efficacy, efficaciousness -- (capacity or power to produce a desired effect; "concern about the safety and efficacy of the vaccine")
       => effectiveness, effectivity, effectualness, effectuality -- (power to be effective; the quality of being able to bring about an effect)