Joke: "Drug Efficacy"

An old man went to see a doctor, and the doctor gave him a medicine and said, "This will last for 12 hours."

The old man nodded his head and left with a smile, the old man walked and laughed, and when he got home, he kept laughing and laughing.

The family was surprised and asked, "What's wrong with you?" The old man said, "What medicine did the doctor prescribe? I had to laugh for twelve hours. I was tired of laughing!"