Abstract: Disclosed is a subdermally implantable drug-delivery device, which contains: a central core extending in an axial direction and having an outer surface and opposing ends, which core includes a matrix of a pharmaceutically effective amount of a subdermally administrable drug substantially uniformly dispersed in a polymeric base material; an intermediate polymeric layer overlying the outer surface of the central core; and an outer polymeric layer overlying the intermediate layer, wherein the intermediate layer controls the rate of diffusion of the drug from the central core to the outer layer. In preferred embodiments, the subdermally administrable drug is a contraceptive agent such as the 16-methylene-17-.alpha.-acetoxy-19-norprogesterone-progestin; the polymeric base material and the outer polymeric layer each contain a polydimethylsiloxane such as Silastic.RTM.; and the intermediate layer contains a porous material such as cellulose.