Five randomised controlled trials (576 patients) and four non-randomised studies (8,358 patients) were included in the review. Risk of bias judgements were reported in the paper, with randomised studies showing mixed results, and non-randomised studies showing generally high risk of bias (where criteria were applicable).
Induction to treatment (five trials; moderate quality evidence): No statistically significant differences were found between naltrexone implants and placebo implants (two trials; Ι²=0%), oral naltrexone (two trials (Ι²=0%), methadone maintenance treatment (one trial), or treatment as usual (one trial).
Retention in treatment (two trials; low quality evidence): Naltrexone implants were significantly more effective than placebo implants (RR 3.20, 95% CI 2.17 to 4.72; two trials; Ι²=84%) and oral naltrexone (RR 3.38, 95% CI 2.08 to 5.49; one trial).
Opioid Use (five trials; low quality evidence): Naltrexone implants were significantly more effective in suppressing opioid use than placebo (RR 0.57, 95% CI 0.48 to 0.68; two trials) or oral naltrexone (RR 0.57, 95% CI 0.47 to 0.70; two trials). Further results at follow-up were reported in the paper.
Non-opioid drug use (four trials; low quality evidence): Non-opioid drug use was significantly more likely in patients with naltrexone implants than those taking oral naltrexone (RR 1.23, 95% CI 1.01 to 1.51; one trial). There were no statistically significant differences between naltrexone implants and other comparators.
Adverse events (moderate quality evidence): Patients with naltrexone implants were significantly more likely than those with placebo implants to report surgical site-related adverse events (RR 4.68, 95% CI 1.63 to 13.44; three trials; Ι²=0%). There were no statistically significant adverse events possibly related to treatment when naltrexone implants were compared with placebo implants (one trial) or oral naltrexone (two trials; Ι²=0%).
Further results (including those incorporating the non-randomised studies) for opioid/non-opioid drug overdose and mortality, were reported in the paper.
No evidence of publication bias was found.