in·ef·fi·ca·cious /(ˌ)ɪˌnɛfəˈkeʃəs/
 (a.)無效力的,無用的
 In·ef·fi·ca·cious a.  Not efficacious; not having power to produce the effect desired; inadequate; incompetent; inefficient; impotent.
    The authority of Parliament must become inefficacious . . . to restrain the growth of disorders.   --Burke.
 Note: ☞ 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.
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 inefficacious
      adj : lacking the power to produce a desired effect; "laws that
            are inefficacious in stopping crime" [ant: efficacious]