Details of her problems have not been released and speculation has been rampant.
But after one student went public with a wild night he spent with Demi Lovato at a house party in Texas in December (10), the star's aides have decided enough is enough.
Brian Payne tells Life & Style magazine he was with Lovato one night when she was "doing line after line (of cocaine) like a pro".
The Texas college student adds, "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."
The star's spokesperson has dismissed reports the rehab stint has any drug connections, stating, "Demi Lovato is not in treatment for drug or alcohol addiction.
"As we have said since she entered treatment last week, Demi decided to seek help for emotional and physical issues she has battled throughout her life. She has taken this step in order to get her life in order.
"While we know many are interested in Demi and her life, we do ask for a modicum of privacy during this difficult time."
The 18 year old has reportedly checked into a facility that specialises in treating adolescents and adult women with a variety of issues, including eating disorders and substance abuse problems.