Inefficacious
Inefficacious , adjective
[Prefix in- not + efficacious: compare French inefficace, Latin inefficax.]
Not efficacious; not having power to produce the effect desired; inadequate; incompetent; inefficient; impotent. — Boyle
The authority of Parliament must become inefficacious... to restrain the growth of disorders.
Ineffectual, says Johnson, rather denotes an actual failure, and inefficacious an habitual impotence to any effect. But the distinction is not always observed, nor can it be; for we can not always know whether means are inefficacious till experiment has proved them ineffectual. Inefficacious is therefore sometimes synonymous with ineffectual.