Objectives: To assess the efficacy and safety of adjuvant therapies in newly diagnosed or relapsing giant cell arteritis (GCA) in terms of relapse rate at week 52 (primary outcome) and to assess the impact of GC tapering regimen on adjuvant effectiveness. Methods: For this systematic review and meta-analysis, we searched PubMed, EMBASE, CENTRAL, trial registries, from inception to November 2020. We included all randomized controlled trials (RCTs) and controlled prospective studies evaluating adjuvant treatments in GCA, without date or language restriction. Two reviewers independently selected studies, extracted data and assessed risk of bias. Quality of evidence was summarised with GRADE. Results: Of the 680 records identified, 16 studies were included (1,068 participants) evaluating various adjuvant therapies compared to GC only. No study compared adjuvants with each other. Risk of bias was high in 5/7 trials evaluating our primary outcome. Risk of relapse at week 52 was reduced for only the anti-IL6 and IL6-receptor drug class versus the control (RR=0.45, 95%CI 0.30-0.66, I2=38%), particularly tocilizumab (RR=0.38, 95%CI 0.23-0.63, I2=42%) with a moderate quality of evidence. We found no significant interaction according to GC tapering regimen. Our meta-analysis did not show a significant benefit for methotrexate. Except for dapsone, ciclosporine and hydroxychloroquine, other adjuvants did not seem to show increased risk of adverse events. Conclusions: Tocilizumab seems to reduce the relapse rate in GCA at week 52 but the quality of evidence was moderate. No other molecule has shown efficacy. No significant interaction on relapse rate by GC tapering regimen was found.