1
Core quality
Capable of producing the intended or desired result; effective.
Example
The treatment was safe and efficacious in the trial.
efficacious
/ˌefɪˈkeɪʃəs/ · ef-ih-KAY-shusadjective
Capable of producing the intended or desired result; effective.
Use efficacious to express this relationship precisely: capable of producing the intended or desired result; effective.
What efficacious Really Means
The word becomes easier to use when its closely related senses are separated and compared.
2
Attributive or predicative use
Use this adjective before a suitable noun or after a linking verb such as be or seem.
Example
Researchers sought the least costly efficacious dose.
3
Analytical distinction
Choose it when this exact descriptive quality matters; a related word may overlap without conveying the same trait.
Example
A remedy may be popular without being efficacious.
Use efficacious Naturally
Notice how the surrounding noun or clause reveals the exact shade of meaning.
The treatment was safe and efficacious in the trial.
Researchers sought the least costly efficacious dose.
A remedy may be popular without being efficacious.
Precision Matters
Efficacious overlaps with several common words, but each carries a different emphasis.
efficacious
vs.Means capable of producing the intended or desired result; effective.
ineffectual
Means failing to produce the intended or desired effect.
efficacious
vs.Means capable of producing the intended or desired result; effective.
detrimental
Means causing harm, damage, disadvantage, or an undesirable effect.
efficacious
vs.Means capable of producing the intended or desired result; effective.
remedial
Means intended to correct a weakness, repair harm, or improve a deficient condition.
efficacious
vs.Means capable of producing the intended or desired result; effective.
beneficially
Means in a way that produces a helpful, favourable, or advantageous result.
Test efficacious in Context
It successfully produced its intended protective result.
1
The vaccine was considered ___ because it consistently prevented the targeted infection.