Miley Cyrus Celebrates 18th Birthday w/ a BONG full of _______! (VIDEO)

In case you missed it, Miley Cyrus celebrated her 18th birthday with a BONG...and what's in the bong is what's causing an up-roar! Sources say she was not smoking marijuana.

The video below was shot during a party at Miley's L.A. area home 5 days after her 18th birthday.

WATCH IT FROM YOUR PHONE - CLICK HERE!



According to a source connected with Miley ... the smoke filling the bong is a natural herb called salvia which has psychedelic qualities. Possession of salvia is legal in California.

As for the video ... the source tells us (and as you can tell) it was shot by one of Miley's friends -- and the theory is someone stole or copied the video from that friend's camera.