Abstract: Implantable devices and methods for delivering pharmaceutical substances into a patient. The implantable device includes the following components: (a) an implant body, (b) a reservoir in the implant body, (c) a heterogeneous composition disposed in the reservoir, which includes a pharmaceutical substance in the solid state contacted by a solution of the pharmaceutical substance, and (d) a nanochannel membrane for delivering the pharmaceutical substance from the reservoir to a patient. Extended, high-quality delivery of low solubility drugs such as hormones and chemotherapeutic agents are achieved.