consisting of desogestrel, 3-ketodesogestrel, or mixtures thereof in the
preparation of a drug delivery system, said drug delivery system characterized by consisting of 28 daily dosage units containing only a progestogenic compound as sole therapeutically effective ingredient.

5. A drug delivery system comprising a package containing 28 daily sequential dosage units consisting essentially of from 70 to 80 micrograms
of a compound selected from the group consisting of desogestrel, 3-
ketodesogestrel, and mixtures thereof