I went through Japanese immigration yesterday. The crew on the inbound flight gave me an extra disembarkation card, so I have a spare in front of me now...
Question 3 on the back of the card asks "Do you presently have in your possession narcotics, marijuana, opium, stimulants, or other drugs, swords, explosives or other such items?"
As I have migraine and pain relief medication with me, and I couldn't remember from last year if they cared about prescription medicine, I left it blank.
At the desk they saw the blank answer and asked.
I asked it the question covered medicine, she asked if it was prescription. After I confirmed it was, she ticked the no box and let me through.