How to say "effectiveness" in Japanese

• 効果こうかJLPT N3approx.Common
  no-adjectiveThe default choice for effectiveness in the general sense of a result or effect that something produces; it covers most everyday uses of the English word.
  彼かれらがいくら弁解べんかいしても彼女かのじょには何なんの効果こうかもなかった。↗

  Their excuses cut no ice with her.
• 利きききCommon
  nounRefers to effectiveness in the sense of how well something works, especially the efficacy of medicine or drink; a narrower noun than 効果.
• 効能こうのうCommon
  nounCovers effectiveness in the sense of the beneficial effects or virtues of a medicine or treatment; it is really a property of medicines rather than actions in general.
  絵画かいがが有ゆうする第だい一いちの効能こうのうは見みる人ひとの目めのごちそうとなることである。↗

  The first virtue of a painting is to be a feast for the eyes.

For most senses of effectiveness, 効果 is the default choice; use 「利き」 for how well something such as medicine works, and 効能 for the beneficial effects or virtues of medicines and the like.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 効果こうかeffect
• 利きききeffectiveness
• 効能こうのうeffect
• 実効性じっこうせいeffectiveness
• 有効性ゆうこうせいvalidity