ObjectiveDespite advances in pharmacology, the treatment of schizophrenia (SZ) remains a challenge due to relapse after antipsychotic discontinuation and multiple adverse effects of antipsychotics. We hypothesized that a low dose of risperidone in combination with sertraline would reduce serious adverse effects without decreasing treatment response. This study aimed to examine the efficacy, safety, and tolerability of low-dose risperidone combined with sertraline to reduce risperidone dose and serious adverse effects in first-episode and medication-naive (FEMN) SZ patients.MethodsA total of 230 patients with FEMN SZ were randomly assigned to receive low-dose risperidone in combination with sertraline (RS group) or regular-dose risperidone (control group). The Positive and Negative Syndrome Scale (PANSS), Hamilton Depression Rating Scale (HAMD), and Personal and Social Performance Scale (PSP) were assessed at baseline and the end of the first, second, third, and sixth months. In addition, serum prolactin levels and extrapyramidal symptoms were measured at baseline and follow-up.ResultsRepeated measures ANCOVA showed significant interaction effects of treatment by time on psychotic symptoms, as well as HAMD, PSP scores, prolactin levels, and extrapyramidal symptoms (all p < 0.05). Compared with the control group, the RS group had greater decreases in PANSS total score and its subscores and HAMD score (all p < 0.01) and a greater increase in PSP total score (p < 0.01). Notably, side effects were lower in the RS group relative to the control group. Improvements in HAMD and PANSS total scores, changes in prolactin levels and gender predicted improvements in PSP from baseline to month 6.ConclusionsOur study suggests that low-dose risperidone in combination with sertraline was more effective for psychotic symptoms and psychosocial functioning, with significantly fewer adverse effects in patients with FEMN SZ.Trial registration number: ClinicalTrials.gov, NCT04076371Supplementary InformationThe online version contains supplementary material available at 10.1186/s12967-023-04272-7.