Britney Spears' ex-husband Jason Alexander alleges the troubled singer started taking drugs in her teenage years.

Alexander, whose brief 2004 marriage to Spears was annulled after 55 hours, tells British magazine Now that the Toxic star was no stranger to illegal substances.

Spears checked into a Malibu, California rehabilitation center last month for unspecified problems following months of incessant partying.

Despite Spears refusing to discuss drug allegations, Alexander recently claimed they had used ecstasy together three years ago.

He tells Now, "She got away with a lot of stuff (when she was younger) because she's Britney Spears.

"She wasn't a virgin when she was dressed up as a schoolgirl in those early videos and she's been taking drugs for eight years.

"If your life's been shaped for you, then you're going to rebel at some point and get confused - and that's where's she's at now.

"Britney first tried drugs when she was 17 or 18. I used to dabble and I knew that she did too, but we never said anything to each other. At least now she's trying to sort it out by going to rehab."