1An as-needed dose or the practice of taking medicine only when symptoms occur; a medicine prescribed for single/occasional use.
熱が出たら頓服を飲むように指示された。
I was told to take a dose as needed if I develop a fever.
医師は必要なら頓服を処方した。
The doctor prescribed an as-needed dose in case it was necessary.
この薬は毎日ではなく頓服で使ってください。
Please use this medicine as needed, not every day.