Synonyms of efficacy

efficacy

noun

ˈe-fi-kə-sē 

as in effectiveness

the power to produce a desired result

questioned the efficacy of the alarms in actually preventing auto theft

Synonyms & Similar Words

• effectiveness
• efficaciousness
• efficiency
• productiveness
• ability
• efficacity
• effectualness
• capability
• edge
• strength
• potency
• capacity
• puissance

Antonyms & Near Antonyms

• ineffectiveness
• inefficiency
• inability
• inadequacy
• ineffectuality
• ineffectualness
• incompetence
• incompetency
• inadequateness

Example Sentences

Recent Examples of efficacy

The study, which focused on people who had undergone surgery to remove a melanoma, tested the drug's efficacy at reducing the risk of the cancer's return. — Megan Cerullo, CBS News, 19 Aug. 2026

The administration gutted the office that tests weapons systems for safety and efficacy. — Jesse Coburn, ProPublica, 19 Aug. 2026

Sweeping multilateral regulatory approaches, such as the EU’s General Data Protection Regulation, are losing their efficacy as other major markets, including China, cease copying the EU playbook. — Mark Leonard, Foreign Affairs, 18 Aug. 2026

Human safety and efficacy must be tested through staged clinical trials, followed by regulatory reviews. — Matthew Kayser, USA Today, 18 Aug. 2026