In the wake of the pop star's controversial "wedding," a source in Britney's hometown of Kentwood, La., made that stunning disclosure.

"Britney has done the drug Ecstasy and smokes marijuana. I know firsthand!" the source -- who passed a polygraph test -- told The ENQUIRER in an exclusive interview.

In the issue that goes on sale Friday, the source describes how Britney becomes "out of control" when she's stoned, reveals her close brush with authorities searching her bags after a flight to Kentwood - and much more.