Britney Spears is allegedly being treated for postnatal depression at the Malibu rehab center she entered last week, the celebrity website TMZ.com has reported.

It said doctors believed that post-childbirth blues were the underlying reason for her substance abuse, though there is also a possibility she could be suffering from bipolar disorder.

The report said doctors believed that Spears was drinking to self-medicate her problem, which has been complicated by an intense feeling that she had lost control of her life.