The 33-year-old actress, who this year starred in a TV adaption of Toyoko Yamasaki's hit novel "Shiroi Kyoto", was arrested in Tokyo on suspicion of possessing ecstasy, although few other details are known, NHK said.
Tear-jerker "1 Litre of Tears" made Sawajiri famous not only in Japan but across Asia with the drama's depiction of its heroine's physical deterioration from a rare disease.
Drug arrests are treated seriously in Japan with celebrities who are caught frequently edited out of movies and TV shows.
The Tokyo police did not immediately respond to a request for comment. Sawajiri's talent agency was not immediately reachable for comment.