Britney Spears is in rehab for substance abuse. She checked in a few days ago somewhere in the United States. Sources with direct knowledge tell TMZ ... people close to the singer had been urging her to check herself in and she finally agreed to do so voluntarily.

As one source put it ... "She realizes she hit rock bottom."



Britney has had issues with drugs -- in particular Adderall -- and alcohol for years. During her many trips to Mexico, she made it a point to replenish her Adderall supply.

Our sources say ... part of the reason she's gone to rehab now is because of her pending DUI case. As one source says, "She knows strategically this will look good in front of the judge -- that she's taking it seriously."

We're told her sons and others have been strongly supportive of the move.

The program is an undetermined length -- they are often 30 days -- but in this case we're told Britney could stay longer for a more meaningful recovery.

On the other hand, back in the day Britney went to rehab several times but bailed after a few days.

what was her last song ?

was only a matter of time

srs

Adderall…?