Demi Lovato fears Miley Cyrus' controversial behaviour is overshadowing the pop star's vocal talent.

Lovato has been friends with the Wrecking Ball hitmaker since they were in their early teens, but admits she is concerned that her pal's saucy stage routines and provocative persona will have a detrimental effect on her credibility as an artist.

She tells U.S. Tv host Katie Couric, "I think she knows what she's doing. A lot of artists take that route of shock value and that's totally fine and that's great, but I think that she has such an incredible voice that's overshadowed by some of the things that she's doing."

Cyrus hit headlines over her racy performance with Robin Thicke at the MTv Video Music Awards in September (13), and courted controversy again by lighting a joint as she accepted a prize at the MTv Europe Music Awards in Amsterdam, Holland earlier this month (Nov13).

Lovato and Cyrus both rose to stardom as teen actresses in Disney productions, Lovato in Tv movie Camp Rock and Cyrus as Hannah Montana, and the Heart Attack hitmaker wants the public to finally let her friend leave her kids Tv persona behind.

She continues, "I think that the world kind of needs to get over the fact that she was Hannah Montana when she was like 16 or whatever... Same thing with me, but I guess my transition was a little different because I went straight to rehab, but - I didn't twerk, I just went to rehab."

Lovato's career hit a stumbling block in 2010 when she was admitted to rehab to deal with a number of personal issues, including a diagnosis with bipolar disorder, self-harm and bulimia. She later bounced back by reviving her music career and landing a role on U.S. reality Tv show The X Factor.