noun
medical efficacy; effect of a medicine
Refers to the therapeutic effectiveness of a drug or medicine. Common in medical, pharmaceutical, and health-related contexts.
この薬の薬効は臨床試験で証明されている。
The medical efficacy of this drug has been proven in clinical trials.
薬効が切れると、また痛みが戻ってきた。
When the effect of the medicine wore off, the pain returned.
Compound of 薬 (medicine) and 効 (effect). The reading やっこう is a regular on'yomi combination.