The Achy Breaky Heart star took to Twitter to express his regret at the teenager's actions.
He wrote: 'I had no idea. Just saw this stuff for the first time myself. I'm so sad. There is much beyond my control right now.'
The video shows the 18 year-old giggling uncontrollably after taking a huge hit of smoke.
Sources told celebrity website that the former Disney starlet was smoking the legal herb salvia - not marijuana.
'Okay, I'm about to lose it now,' Cyrus says in the video, after taking her first hit. 'I'm having a little bit of a trip right now.'