also: こうげん
noun
Refers to the beneficial result or power of something, such as a medicine, treatment, or method. Somewhat formal and often used in written contexts.
この薬の効験は臨床試験で証明された。
The efficacy of this medicine was proven in clinical trials.
新しい治療法の効験が期待されている。
The effectiveness of the new treatment is anticipated.
Obsolete kana usage; the modern reading is こうけん.
効果 is the common, everyday word for 'effect' or 'result'. 効験 is more formal and specifically emphasizes proven beneficial power, often used in medical or technical contexts.
効能 also means 'efficacy' but is more commonly used for the beneficial effects of medicines, hot springs, or health products. 効験 is less common and slightly more formal.
Compound of 効 (effect, efficacy) and 験 (test, effect). The exact historical derivation is uncertain, but the combination naturally conveys 'proven effectiveness'.