Immediate effect; something that works instantly (often used for medicines or methods).
この鎮痛薬は即効で痛みが和らぐ。
This painkiller relieves pain immediately.
宣伝では『即効』と書かれているが、個人差がある。
Although the advertisement says 'instant effect', there are individual differences.
問題を解決するための即効的な対策を講じた。
They took an immediate measure to solve the problem.