"Teen Mom" star Amber Portwood just left an Indiana courtroom ... where she was accused of violating her probation ... and TMZ has learned it all has to do with drugs and TWO no-shows for urine tests.
Law enforcement sources tell TMZ ... Portwood was popped on Dec. 16 for possession of a controlled substance. It's unclear what the substance was.
Sources also tell us Portwood "failed to provide urine drug screen on Dec. 16 and Dec. 19."
Portwood is also on the hook for various other alleged violations -- including failure to complete an anger management class and failure to set up a college fund for her daughter.
Today, Amber was ordered to remain in custody until her next hearing in late January.