Thirteen studies were included in the review (1,395 patients: 739 in standard dose groups, 457 in low dose groups and 199 in very low dose groups). Most studies had follow-up of at least one year.
There was no significant difference in the rate of overall treatment failure, relapse or hospitalisation between standard dose and low dose groups.
Compared with standard dose treatment, very low dose treatment was associated with a significant increase in the rate of overall treatment failure (RD 0.14, 95% CI 0.02 to 0.26, NNH=8, 95% CI 4 to 50; six RCTs), hospitalisation (RD 0.11, 95% CI 0.04 to 0.17, NNH=9, 95% CI 6 to 25; five RCTs) and relapse (RD=0.26, 95% CI 0.12 to 0.41, NNH=4, 95% CI 3 to 8; six RCTs).
No significant difference was found between standard dose group and low dose group or very low dose group in the rate of drop-outs due to side effects.
Significant heterogeneity was observed only in the outcome of relapse for the comparison between very low dose and standard dose groups (Ι²=59%). Subgroup analyses on patients who received depot antipsychotics showed similar results. No evidence of publication bias was found for efficacy outcomes.