Inefficacious

Antonyms for inefficacious:

effective, efficacious.

Synonyms for inefficacious:

Sense 2

ineffectual, ineffective.

Sense 4

inefficient.

Sense 5

useless.

incapable

unable.

unrealistic

impractical.

Other synonyms and related words:

empty, unavailing, unable, useless, otiose, profitless, unproductive, vain, impractical, feckless, inefficient, ineffectual, unprofitable, abortive, counterproductive, inexpedient, ineffective, unsuccessful, Hamstrung, fruitless, bootless, futile, barren.

ineffectual (adjective)

bootless, fruitless, ineffective, unsuccessful, unavailing, barren, unproductive, feckless, inefficient, useless, abortive, vain, futile, unable, unprofitable.

vain (adjective)

profitless.

defeated (verb)

unsuccessful.

Usage examples for inefficacious:

• It is a sort of tenderness that is quite inefficacious. - "The Duke's Children", Anthony Trollope.
• Unhappily it proved inefficacious. - "The Inside Story Of The Peace Conference", Emile Joseph Dillon.