Translation guide
The chemical stimulant found in coffee, tea, and other products. In Japanese, it is most commonly referred to as カフェイン, a loanword from English.
カフェイン
caffeine
Referring to the chemical compound itself, or its presence in food/drink.
The standard Japanese word for caffeine, used in all contexts. A katakana loanword from English.
コーヒーにはカフェインが含まれています。
Coffee contains caffeine.
カフェインの取りすぎに注意してください。
Please be careful not to consume too much caffeine.
A rare, technical term for caffeine, literally 'tea element'. Almost never used in everyday language.
茶素はアルカロイドの一種です。
Caffeine is a type of alkaloid.