Aims To describe drug use and safety with intramuscular injectable extended‐release naltrexone (XR‐NTX) in opioid dependence during a 1‐year open‐label extension phase. Design Following 6 months of randomized, double‐blind, placebo (PBO)‐controlled injections given every 28 days, patients receiving XR‐NTX 380 mg continued and PBO patients were switched to open‐label XR‐NTX, with monthly individual drug counseling, for a further year. Setting Thirteen clinical sites in Russia. Participants Adult opioid‐dependent outpatients. Measurements Monthly urine samples; reports of craving and functioning; adverse events. Findings For the open‐label extension (n = 114), 67 continued on XR‐NTX and 47 switched from PBO during the double‐blind phase to XR‐NTX during the open‐label phase. Overall, 62.3% (95% CI: 52.7%, 71.2%) completed the extension. Discontinuation occurred most commonly because of withdrawal of consent (18.4%) and loss to follow‐up (11.4%); two patients discontinued as a result of lack of efficacy and one because of adverse events. Urine testing revealed that 50.9% (41.5%, 60.4%) were abstinent from opioids at all assessments during the 1‐year open‐label phase. Adverse events reported by 21.1% of patients were judged to be study drug‐related. Injection site reactions were infrequent (6.1%) and the majority were mild. Elevations in liver function tests occurred for 16.7% of patients, but none of these elevations was judged to be clinically significant. No patients died, overdosed or discontinued as a result of severe adverse events. Conclusions During a 1‐year open‐label extension phase of injectable XR‐NTX for the prevention of relapse in opioid dependence, 62.3% of patients completed the phase and 50.9% were abstinent from opioids. No new safety concerns were evident.