An efficacious symbol is something that promotes an idea, but at the same time it actually causes that idea to happen. For example, the Church is one because it "promotes" salvation, but it also "causes" salvation.
That medicine is efficacious in treating a cold
The word efficacious means about the same as "effective" -- it means capable of having the intended result. Example: "A shotgun is efficacious in controlling wild rabbits." "For a simple cough, honey is often as efficacious as medicinal syrups."
(Capable of having a desired effect or result, effective.)"The medicine is efficacious in stopping a cough.""The farmers were looking for a chemical that would be efficacious against the corn fungus."
productive, efficient, effective
Quinine
Useful, of course, but also handy, utile, efficacious, productive
successful, efficacious, useful
B12
Effective, effectual, efficacious, productive, industrious.
efficacious - having strong swaying power or hindering the the behaviors of others.
The belief that political involvement can bring about change
acknowledged, at the top of the tree, best- selling, booming, efficacious, favourable, flourishing, fortunate, fruitful.