Participants will be recruited from the AIDS and addiction programs and who meet study admission criteria will be stratified within each site according to baseline viral load (>100,000 copies/<100,000 copies) and CD4 count (>50/<50 copies). Participants will be randomized to a treatment condition, receive a naloxone challenge, and if pass be prescribed oral naltrexone or oral placebo and implant/implant placebo), and given a schedule for addiction counseling and HIV treatment appointments. A 2-week supply of oral medication will be provided at each bi-weekly counseling session, and will be re-implanted at weeks 12, 24, and 36. Only the research pharmacist will know the group assignments, however the blind can be broken in case of emergency.