Japan has other surprise drug policies. For example, the prescription drug Adderall is banned because it contains amphetamine.
https://jp.usembassy.gov/u-s-citizen-services/doctors/import...
This article is enlightening in Japan's attitude towards these stimulants. But I could go any convenience store and pick up bottles of "genki" (energy) drinks. There doesn't seem to be much regulations and only the occasional news story of people overdosing.