efficacy

n.

1.

Power to produce effects; operation or energy of an agent or force; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer.

Noun

1.

efficacy - capacity or power to produce a desired effect; "concern about the safety and efficacy of the vaccine" Synonyms: efficaciousness Antonyms: inefficaciousness, inefficacy - a lack of efficacy

effectiveness, effectivity, effectuality, effectualness, efficacious, efficaciousness, inefficacious, inefficaciousness, inefficacy