OTC medicine is plenty available in Japan, but it's hard to match it to what you know in your home country. Reading Katakana helps a lot and having studied Chemistry too, but it would be so nice to get a nice English overview of various  Japanese OTC medicine.

Luckily someone did that: https://lifeabroad.jp/html/medical_health/otc.html

Of course do not take that web page as the definite truth and cross-check the ingredients and dosage.