Definition of efficacious in US English:

efficacious

adjective

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

    ‘the vaccine has proved both efficacious and safe’
    • ‘So the same event or object can have a number of properties, not all of which are efficacious in bringing about the same effect.’
    • ‘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.’
    • ‘No difference was noted concerning one tradition being more powerful or efficacious than any other.’
    • ‘This process has resulted in the designation of many psychotherapy treatments as being efficacious.’
    • ‘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.’
    • ‘During this era, biological discovery is accelerating, resulting in the development of safer and more efficacious drugs.’
    • ‘There may be occasions, for instance, when a dose of old-fashioned common sense can be as efficacious as a more sophisticated remedy.’
    • ‘A small comparison study demonstrated that these two drugs are equally efficacious.’
    • ‘We want to know that what we do is not merely efficacious but right.’
    • ‘When contemporary arts are produced for an international market, they can still be efficacious.’
    • ‘The use of allogenic tissue in orthopaedic surgery is generally safe and efficacious.’
    • ‘History and theory show that the use of naked government aggression is not a moral or efficacious way of dealing with poverty.’
    • ‘The vaccine was presumed to be safe and efficacious.’
    • ‘Both drugs were equally efficacious in improving auditory hallucinations and suspiciousness.’
    • ‘Second, proving that a supposedly life extending drug will be efficacious is an extremely difficult task.’
    • ‘It may not mean that the ultimate result is not efficacious.’
    • ‘These drugs may be used topically or systemically and are safe and efficacious.’
    • ‘The ultimately most efficacious way is to change a group belief is from within.’
    • ‘This brings us to another question: are we using our existing personnel in the most efficient and efficacious way?’
    successful, effectual, productive, constructive, fruitful, functional, potent, powerful
    effective, successful, effectual, productive, constructive, fruitful, potent, powerful
    View synonyms

Origin

Early 16th century: from Latin efficax, efficac- (from efficere ‘accomplish’: see effect)+ -ious.

Pronunciation

efficacious

/ˌefəˈkāSHəs//ˌɛfəˈkeɪʃəs/