The clip, which is believed to have been recorded by a pal at her 18th birthday – shows the star inhaling what is believed to be the legal hallucinogen salvia divinorum.
Friend Anna Oliver has been forced to close down her Twitter account thanks to the backlash of fans who are angry she recorded the film in the first place – although it is still not known how the footage made it to the internet.
But according to TMZ, Cyrus has brushed off the controversy surrounding the tape, insisting she is 'just young and having fun'.
A source told the site: 'Miley doesn't care. She's filming her movie and getting on with her life.'