The ideal naltrexone sustained-release delivery system should be easy to inject or implant, not cause adverse tissue reaction, release the drug at a relatively constant rate for at least 30 days, and biodegrade within a short time afterwards. Mechanisms which can be used for sustaining drug release include reducing solubility and surface area, coating, encapsulation and microencapsulation, complexation, binding and hydrophilic gelation. Drug release from such systems is controlled by diffusion through a barrier/film, diffusion from a monolithic device, erosion of the surface, hydrolysis, ion exchange, biodegradation, or a combination of these. Injectable systems would seem to be ultimately preferred because of the ease of administration and handling, while the implantable devices may find first use in man since they are easily removable, should that be necessary. Maintaining particulate-free products and sterilization methods are two problems with all parenteral dosage forms. Production must be particularly well controlled and validated.