What are the opposite words for efficacy?

The term "efficacy" refers to the ability of something to produce a desired result. Antonyms for efficacy are ineffectiveness, inefficiency, inadequacy, impotence, futility, weakness, and uselessness. Ineffectiveness implies a total lack of ability to achieve a goal. Inefficiency refers to the inability to achieve a goal with minimum effort or resources. Inadequacy suggests that something falls short of what is required or expected. Impotence refers to a lack of power or authority to bring about change. Futility implies that something is pointless or hopeless. Weakness means a lack of strength, and uselessness suggests that something has no practical value.

Antonym of the day

were one back
aid, discourage, dissuade.