useful vs efficacious

useful and efficacious both are adjectives.

Word	Noun	Adjective	Verb	Adverb
useful	No	Yes	No	No
efficacious	No	Yes	No	No

useful (adjective)	efficacious (adjective)
being of use or service	marked by qualities giving the power to produce an intended effect
having a useful function	producing or capable of producing an intended result or having a striking effect