The purpose of this clinical trial is to study the efficacy and safety of naltrexone implants as relapse prevention for patients that are completing treatment for opiate addiction in inpatient (or similarly controlled) settings. Participants volunteer for the study before being released from inpatient treatment, and are randomized to a naltrexone implant group or a waiting-list control for the duration of the first six months following completion of inpatient treatment. Both groups are free to receive treatment as usual (TAU) from the Norwegian healthcare system. After six months, both groups will be offered to have naltrexone implanted for the remaining six months of the study.

The hypotheses are that quality of life, depression, opioid use, will be significantly better in the naltrexone group compared to the non at 6-month follow-up. For the last six months of the trial, the investigators hypothesise that choice of naltrexone implant will mainly strengthen positive tendencies or reverse negative trends on the aforementioned variables.

The investigators also hypothesize that the implants can prevent death from opioid overdose up to 6 months after commenced treatment.

Inclusion Criteria:

• soon to complete inpatient treatment for opioid addiction
• living in southern Norway

Exclusion Criteria:

• psychosis/major depression, currently not treated
• pregnancy
• liver enzymes: ASAT or ALAT > threefold above upper boundary
• maintenance treatment with methadone or buprenorphine