Japan has some of the strictest drug laws in the world, and many common over-the-counter (OTC) medications found in Western pharmacies are strictly prohibited or heavily regulated. The most significant category of banned drugs includes those containing pseudoephedrine or codeine. Common cold and sinus medications like Sudafed, Vicks VapoInhaler, and some versions of NyQuil are illegal because they contain stimulants or narcotics that are classified as controlled substances in Japan. Even a small amount can lead to detention or deportation. Additionally, some inhalers and allergy medications containing prohibited ingredients are banned. If you need to bring a 30-day supply of a permitted but strong medication, you may need a "Yunyu Kakunin-sho" (import certificate). For standard painkillers like Ibuprofen (Advil) or Acetaminophen (Tylenol), they are generally allowed for personal use, but it is best to keep them in their original packaging. Always check the official Ministry of Health website before traveling, as "ignorance of the law" is not a valid defense in Japanese courts regarding prohibited substances.