A drug delivery system also intended as unit dosage form comprising a thin water-soluble film matrix, wherein said film matrix comprises a) a polyvinyl alcohol-polyethylene glycol graft copolymer (PVA-PEG graft co-polymer) as a water-soluble matrix polymer； an active ingredient being a steroid in which the positions 6 and 7 of the steroidal skeleton are both a &mdash；CH2&mdash； residue； and said film matrix has a thickness of less than 300 &mu；m.
