efficacious

/ɛf.ɪ.ˈkeɪ.ʃəs/adjective

Able to produce the intended result; working well.

Example sentence

“The new treatment proved efficacious in most of the patients tested.”

Formal and technical; medicine and pharmacology keep it alive. Everyday English says 'effective', and the related noun is 'efficacy'.

Related words

effortlessDone easily, without needing to try hard.effervescentLively, cheerful, and overflowing with energy and enthusiasm.effusiveExpressing feelings, especially praise or gratitude, in an overflowing and unrestrained way.effaceTo rub out or wipe away something written or marked, making it impossible to read or see.egregiousStanding out as remarkably bad; shockingly obvious in a negative way.educatorSomeone whose work is teaching others, especially a person known for it.