expression, godan verb (-ru, irregular)
be effective; be beneficial; have an effect
Expresses that something produces a desired result or is good for a purpose. Often used in contexts like medicine, methods, or advice.
この薬は風邪に効がある。
This medicine is effective for colds.
毎日の運動は健康に効がある。
Daily exercise is beneficial to health.
効く is a more common, single-word verb meaning 'to be effective'. 効がある is a slightly more formal or explanatory expression.
効果がある is a more common and neutral expression for 'to be effective'. 効がある is a bit more literary or formal.
Compound of 効 (kō, 'effect') + が (subject marker) + ある (aru, 'to exist'), literally 'there is an effect'.