Must not do
This pattern is used to indicate that something is prohibited or must not be done.
Exemplos
無駄に時間を使ってはいけない。
You must not waste time.
ここで大きな声を出してはいけない。
You must not raise your voice here.
薬を適切に使ってはいけない。
You must not use the medicine improperly.
Verificação rápida
Você não deve perder tempo. (無駄に時間を使っ___はいけない。)