The use or possession of some common prescription and over-the-counter medicines are banned under Japan’s strictly enforced anti-stimulant drugs law. This includes Vicks inhalers, medicines for allergies and sinus problems and even some mild painkillers like those containing codeine. Customs officials may not be sympathetic if you claim ignorance.
If in any doubt, check with the nearest Japanese Embassy or Consulate before you travel.
Taking prescribed medication into Japan for personal use, ie. to treat an established and ongoing medical condition:
Drugs, syringes, cosmetics and medical devices for personal use can be imported up to the limit of 1 month’s supply, without any special permission.
For amounts over the limit, or for certain substances, a special authorisation is required (Yakkan Shoumei – the Import Report of Medication”). This must be applied for and obtained before travel, and taken with you to Japan.
Full details from Japan’s Ministry of Health, Labour and Welfare: www.mhlw.go.jp