Webster 1913 Edition
Lack of power to produce the desired or proper effect; inefficiency; ineffectualness; futility; uselessness; fruitlessness;
inefficacyof medicines or means
inefficacywas soon proved, like that of many similar medicines.
Webster 1828 Edition
1.Want of power to produce the desired or proper effect; inefficiency; as the inefficacy of medicines or of means.
2.Ineffectualness; failure of effect.