BACKGROUND: Readmissions to hospital due to medication-related problems are common and may be preventable. Pharmacists act to optimise use of medicines during care transitions from hospital to community. OBJECTIVE: To assess the impact of pharmacist-led interventions, which include communication with a primary care physician (PCP) on reducing hospital readmissions. METHODS: PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CINAHL and Web of Science were searched for articles published from inception to March 2021 that described interventions involving a pharmacist interacting with a PCP in regards to medication management of patients recently discharged from hospital. The primary outcome was effect on all-cause readmission expressed as Mantel-Haenszel risk ratio (RR) derived from applying a random effects model to pooled data. Sensitivity analysis was also conducted to investigate differences between randomised controlled trials (RCTs) and non-RCTs. The GRADE system was applied in rating the quality of evidence and certainty in the estimates of effect. RESULTS: In total, 37 studies were included (16 RCTs and 29 non-RCTs). Compared to control patients, the proportion of intervention patients readmitted at least once was significantly reduced by 13% (RR = 0.87, CI:0.79-0.97, p = 0.01; low to very low certainty of evidence) over follow-up periods of variable duration in all studies combined, and by 22% (RR = 0.78, CI:0.67-0.92; low certainty of evidence) at 30 day follow-up across studies reporting this time point. Analysis of data from RCTs only showed no significant reduction in readmissions (RR = 0.92, CI:0.80-1.06; low certainty of evidence). CONCLUSIONS: The totality of evidence suggests pharmacist-led interventions with PCP communication are effective in reducing readmissions, especially at 30 days follow-up. Future studies need to adopt more rigorous study designs and apply well-defined patient eligibility criteria.