Efficacious

[Sarah]

Possessing the quality of being effective; productive of, orpowerful to produce, the effect intended; as, an efficacious law.

[Sarah]

A douchey way of saying effective.

[Sarah]

An adjective (descriptive word):
Describing thing, or person, producing, or sure to produce, desired effect.
Efficaciously (adverb) describing the behaviour of act in such a manner as to effect the desired effect.
I may help to understand that the Latin root for these words is the same as that for Efficient.

[Marquetta]

able to produce the intended result

[Jessica]

(of something inanimate or abstract) successful in producing a desired or intended result; effective.