Drug delivery systems and biocompatible coatings for use with implantable stimulation devices such as cochlear implants have been developed. These drug delivery systems and coatings comprise polyhydroxyalkanoate (PHA) polymers and copolymers. The drug delivery systems may be used to deliver pharmacologically active substances, for example, directly from a cochlear implant to the inner ear. The coatings can impart lubricity to cochlear devices for ease of insertion of the electrodes. In the preferred embodiment, the drug delivery system comprises a polyhydroxyalkanoate polymer, and in the most preferred embodiment, the PHA polymer comprises poly(4-hydroxybutyrate) (P(4HB)) or copolymer thereof. A particularly preferred embodiment is where the silicone sheath of the cochlear implant electrodes has been surface modified, and coated with P(4HB), and the P(4HB) either contains a pharmacologically active substance or has been coated with such a substance.