Britney Spears has been taken to hospital for a clinical evaluation following a dispute at her home over the custody of her children.
Los Angeles Police Department spokesman Officer Jason Lee said police arrived at Spears' hilltop home in Studio City at 8pm PST last night (0400 GMT Friday).
He said police had tried "to resolve the dispute peacefully and legally", according to the court order governing Spears' two sons with Kevin Federline.
People magazine's website reports that after nearly three hours, police determined that the court order stated that the children were supposed to be with Federline and a transfer was arranged.
Lee later said: "While officers were on the scene, they observed Ms Spears under the influence of an unknown substance. She is now being taken in for an evaluation, more than likely to a hospital. There were no reported injuries to anyone involved including the children."
Twenty-six-year-old Spears lost primary custody of her two sons in October.
