efficacy

noun

ef·​fi·​ca·​cy ˈe-fi-kə-sē 

plural efficacies

: the power to produce an effect

Synonyms

• edge
• effectiveness
• effectualness
• efficaciousness
• efficacity
• efficiency
• productiveness

Examples of efficacy in a Sentence

In the planner's view, Rumsfeld had two goals: to demonstrate the efficacy of precision bombing and to "do the war on the cheap." —Seymour M. Hersh, New Yorker, 7 Apr. 2003

Vaccines exist, but their efficacy against aerosolized plague is unknown. —Sharon Begley et al., Newsweek, 8 Oct. 2001

… efficacy does not have to be demonstrated before homeopathic products are marketed. —Alison Abbott et al., Nature, 26 Sept. 1996

questioned the efficacy of the alarms in actually preventing auto theft

Recent Examples on the Web

The Silicon Valley investor has called for major reform at the FDA in the past and argued that the efficacy of drugs should be measured after they have been allowed on market. —Sara Dorn, Forbes, 9 Dec. 2024

While no negative side effects were reported, the team says that further trials will need to be conducted to ensure the safety and efficacy of the technique. —Michael Irving, New Atlas, 8 Dec. 2024

While there is extensive research on the safety and efficacy of creatine, most of the studies were conducted on male athletes. —Anna Giorgi, Verywell Health, 6 Dec. 2024

Exactly what accounts for this trend is unclear, experts say, and scientific research on the benefits and efficacy of gender dysphoria treatments is mixed. —Henry Gass, The Christian Science Monitor, 2 Dec. 2024

Word History

Etymology

borrowed from Latin efficācia, from efficāc-, efficāx "capable of fulfilling a function, efficacious" + -ia -y entry 2

First Known Use

1527, in the meaning defined above

Kids Definition

efficacy

noun

ef·​fi·​ca·​cy ˈef-i-kə-sē 

plural efficacies

: the power to produce a desired result