Synonyms for Efficacious:

adj.

effective (adjective)
study at effective, productive.
efficient, productive (adjective)
effectual, useful, effective.

n.

functional, high-powered, worthwhile, practical, valuable, useful, helpful. thrive, productive. efficacious (noun)
impelling, trenchant, impressive, hard-hitting, rough-and-ready, telling, effective, effectual.

Other synonyms:

productive. useful
helpful.
Other relevant words:
practical, valuable, helpful, thrive, useful, high-powered, productive, effective, worthwhile, functional.

Usage examples for efficacious

  1. How to insure that it would be efficacious – Witch-Doctors by Charles Beadle
  2. A droll fellow was Joe at times, for under his sobriety lay much humor; and I soon discovered that a visit from him was more efficacious than other cordials in cases of despondency and discontent. – Kitty's Class Day And Other Stories by Louisa M. Alcott
  3. It seems a simple precaution, and any one so minded might well do the same under similar circumstances, provided he thinks the proceeding efficacious – Castles and Chateaux of Old Touraine and the Loire Country by Francis Miltoun