Demi Lovato has been accused of being a heavy drinker and cocaine user.

The 18-year-old Disney singer and actress was recently admitted to rehab with "emotional and psychological issues", and a source claims her wild partying ways may have contributed to her present state.

US college student Brian Payne said he witnessed Demi snorting cocaine at a party, after they had both been to see band Neon Indian in her hometown, Dallas, just after Christmas last year.

He told "She was doing line after line like a pro - and she was 17 at the time.

"I just remember her doing it as if she had been doing it for a long time. It didn't seem like something new to her."

Another source close to the 'La La Land' singer said she has dealt badly with her recent split from pop singer Joe Jonas - whom she was performing on tour alongside at the time she was admitted to rehab.

The source said: "Demi's been on a tear lately. She'll chug booze straight from the bottle (sic)."

Demi's family have yet to respond to allegations she is a heavy drinker or cocaine user, but her estranged father, Patrick Lovato, previously said he blames the pressures of fame were "one of the things I worried about when she signed with Disney."

Other members of Demi's family have, however, blasted Patrick; saying he "knows nothing" about his daughter, and she herself said last year she hadn't spoken to him for two years.