noun[mass noun] • formal
- The ability to produce a desired or intended result: there is little information on the efficacy of this treatmentMore example sentences
- It'll be some time before the safety and efficacy of the other products is proven.
- The power of transformation or efficacy of the commodity is often a selling point.
- Blood tests may be needed periodically to monitor the treatment and its efficacy.
early 16th century: from Latin efficacia, from efficax, efficac- (see efficacious).