谁愿意帮我解释以下这个英语笑话?
A DISTRAUGHT PATIENT phoned her doctor's office.Was it true,the woman wanted to know,that the medication the doctor had prescribed was for the rest of her life?She was told that it was.There was a moment of silence before the woman continued,"I'm wondering,then,just how serious my condition is.This prescription is marked 'no refills'."
主要是最后的“no refills”是什么意思