Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Retention in treatment
[42] Systematic review	203 people 2 RCTs in this analysis	Proportion of people retained in treatment 26/50 (52%) with naltrexone 15/33 (45%) with placebo	RR 1.18 95% CI 0.72 to 1.91 P = 0.51		Not significant
[43] Systematic review	40 people Data from 1 RCT	Proportion of people retained in treatment 15/22 (68%) with high-dose naltrexone 7/18 (39%) with placebo	RR 1.75 95% CI 0.92 to 3.34 P = 0.88		Not significant
[43] Systematic review	38 people Data from 1 RCT	Proportion of people retained in treatment 12/20 (60%) with low-dose naltrexone 7/18 (39%) with placebo	RR 1.54 95% CI 0.78 to 3.05		Not significant