Britney Spears picked up the bottle, started having sex and experimented with drugs -- all before turning sweet 16, her mom will allegedly claim in a new tell-all book set to rock the troubled star's shaky psyche.

Lynne Spears, 53, doesn't hold back in "Through the Storm," according to The Sun, which obtained a leaked copy of the memoir. In it, she supposedly claims Britney started drinking when she was only a 13-year-old Mousketeer and that she had sex with a high school senior when she was only 14. Of course, this would put down previous reports that she lost her virginity to Justin Timberlake.

In the book, the elder Spears reportedly admits allowing her daughter, now 26, to sleep with Timberlake when she was only 16 because she "was in love and Justin was good for her," a source told The Sun.

As for the habit that has dragged her down over the last few years? Mother Spears says her daughter first started taking drugs at 15 when she was recording her blockbuster debut, "bouncing baby One More Time."

The book also alleges that Britney, then 16, was caught with cocaine and marijuana on a private jet.

According to the leaked book, Lynne Spears expresses regret for handing over control of her daughters' affairs to business managers and allowing her to become exploited as a worldwide sex symbol at such a young age.

Not surprisingly, mother and daughter are currently estranged. The book is due on Sept. 16. (From AOL News)