Fig. 1: Forest plot.

Hedges’ g is the effect size and indicates the standardised mean difference in social connectedness between the naltrexone and placebo conditions. Circles indicate individual study effects and error bars indicate their corresponding 95% confidence intervals. The diamond indicates the average effect size and corresponding 95% confidence interval obtained with the three-level random-effects meta-analysis. Negative effect sizes indicate lower social connectedness after administration of naltrexone than after administration of placebo. The vertical dotted line indicates an effect size of Hedges’ g = 0 (i.e., no difference in social connectedness between the naltrexone and placebo conditions).