…a book in her hand, which she was unable to read, or in lying, weary and languid, on a sofa, did not speak much in favour of her amendment; and when, at last, she went early to bed, more and more indisposed, Colonel Brandon was only astonished at her sister’s composure, who, though attending and nursing her the whole day, against Marianne’s inclination, and forcing proper medicines on her at night, trusted, like Marianne, to the certainty and efficacy of sleep, and felt no real alarm.
There are no more uses of "efficacy" in the book.
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The doctor weighed the efficacy of each treatment against potential side-effects.
They held hearings to investigate concerns about the safety and efficacy of the vaccine.