They aren’t road legal by EU laws either, although there are a hand full of owners from EU countries (Poland, Czech Republic, Austria) that managed to get theirs registered through exceptions.

https://www.degruyter.com/document/doi/10.1515/pz-2024-2017/html?srsltid=AfmBOop4bYqn5BhUClAYyvICkeuID7a9Tqh7YZyf9JKnKAJyNQhgt0zS

The title of the study is “In a narcotic trance, or stimulants in Germanic communities of the Roman period”

Its literally the first result if you Google “Praehistorische Zeitschrift Stimulants”. It’s pretty easy to find.