Teen Mom Star Amber Portwood Arrested

TMZ has obtained a police report that reveals new details about Amber Portwood's arrest last week -- turns out the controlled substances she was busted for were a variety of prescription pills ... most of which she couldn't produce prescriptions for.

As TMZ first reported, the "Teen Mom" star was popped back on December 19 on the possession charge as well as failing to provide a urine sample (which is part of her probation).

According to an affidavit given by Sgt. John Branson of the Anderson Police Department, the probation department visited Amber's home on December 16 because she had missed her probation appointment that day. Sgt. Branson says the probation officers found Portwood to be "very groggy."