1. Effectiveness. Likelihood of achieving desired end by expending effort. Example: Evaluate changes for their efficacy to produce desired result; if unsure the changes will do the job, reevaluate our plan. 2. Medicine: A treatment’s or vaccine’s effectiveness in curing, preventing, or lessening the effects of a disease or illness.

More On This Topic

Link to This Definition
Did you find this definition of EFFICACY helpful? You can share it by copying the code below and adding it to your blog or web page.
Written and fact checked by The Law Dictionary