What rhymes with efficacious? These are words that rhyme with efficacious. See also Rhyme Poems and How many syllables are in efficacious?
gracious, spacious
audacious, capacious, ceraceous, cretaceous, fallacious, flirtatious, hellacious, herbaceous, horatius, ignatius, loquacious, predaceous, salacious, sebaceous, tenacious, vexatious, vivacious, voracious
efficacious, ostentatious