'Teen Mom' Amber Portwood -- I Need Prison to Save My Life

"Teen Mom" star Amber Portwood thinks prison is the only way to save her life from a brutal drug addiction, TMZ has learned.

Sources tell us, immediately following the reality TV star's incarceration, her last drug test came back positive for the opiate-based drug Suboxone ... a highly addictive drug similar to Morphine.

Law enforcement sources tell us, Portwood admitted she can't control herself around the drug -- even buying it off the street during her court-ordered drug program.

We're told Amber believes prison is the only way to get clean because it will force her to kick the addiction cold turkey.

Portwood is currently locked up and a judge will decide her sentence in the next couple of weeks.