Synonyms of inefficacious

1 Syllable
null, vain, lame, void
2 Syllables
shucker, idle, paltry, inept, barren, fruitless, worthless, feeble, nuller, bootless, feckless
3 Syllables
inferior, impotent, limited, forceless, time-wasting, spineless, useless, futile, innocuous, withered, unfruitful, unable, slack-spined, nonviable, impuissant, powerless
4 Syllables
abortive, unavailing, improficient, nugatory, unnotable, impractical, unsanctioned, unsuccessful, incompetent, defeasible, infeasible, neutralized, inefficient
5 Syllables
unnegotiable, invertebrate, unworkmanlike, unprofitable, inadequate, unproductive, indecisive, ineffective, anticlimactic, unserviceable
6 Syllables
unbusinesslike, inoperative