Definition of efficacious in US English:



  • (of something inanimate or abstract) successful in producing a desired or intended result; effective.

    ‘the vaccine has proved both efficacious and safe’
    • ‘Second, proving that a supposedly life extending drug will be efficacious is an extremely difficult task.’
    • ‘So the same event or object can have a number of properties, not all of which are efficacious in bringing about the same effect.’
    • ‘During this era, biological discovery is accelerating, resulting in the development of safer and more efficacious drugs.’
    • ‘This brings us to another question: are we using our existing personnel in the most efficient and efficacious way?’
    • ‘It will prove efficacious to plant trees, shrubs and herbaceous plants in the autumn because they will get their roots down faster during their first wet winter.’
    • ‘There may be occasions, for instance, when a dose of old-fashioned common sense can be as efficacious as a more sophisticated remedy.’
    • ‘History and theory show that the use of naked government aggression is not a moral or efficacious way of dealing with poverty.’
    • ‘The use of allogenic tissue in orthopaedic surgery is generally safe and efficacious.’
    • ‘It may not mean that the ultimate result is not efficacious.’
    • ‘These drugs may be used topically or systemically and are safe and efficacious.’
    • ‘No difference was noted concerning one tradition being more powerful or efficacious than any other.’
    • ‘A small comparison study demonstrated that these two drugs are equally efficacious.’
    • ‘This process has resulted in the designation of many psychotherapy treatments as being efficacious.’
    • ‘Both drugs were equally efficacious in improving auditory hallucinations and suspiciousness.’
    • ‘We want to know that what we do is not merely efficacious but right.’
    • ‘Most of these drugs are efficacious and have enormously enhanced the power of the physician to treat and cure disease.’
    • ‘Clinical trials are in progress and research is ongoing for developing a safe and efficacious vaccine against the disease.’
    • ‘The vaccine was presumed to be safe and efficacious.’
    • ‘The ultimately most efficacious way is to change a group belief is from within.’
    • ‘When contemporary arts are produced for an international market, they can still be efficacious.’
    successful, effectual, productive, constructive, fruitful, functional, potent, powerful
    effective, successful, effectual, productive, constructive, fruitful, potent, powerful
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Early 16th century: from Latin efficax, efficac- (from efficere ‘accomplish’: see effect)+ -ious.