Background: Scaling and root planning (SRP) is the gold standard for non-surgical periodontal treatment. Green tea as a supporting alternative in non-surgical periodontal treatment has been suggested as a therapeutic option in the treatment of periodontitis. Objective: To analyse the comparative effectiveness of green tea (Camellia sinensis) in its different forms and applications for the treatment of periodontitis. Methods: We included randomized clinical trials evaluating green tea as an adjuvant therapeutic agent to scaling and root planning (SRP) in the treatment of periodontitis. For the meta-analysis, we calculated standardized mean difference (SMD) and 95%CI comparing green tea and control (only SRP). We subgrouped by types of application forms of green tea. The certainty of the evidence was assessed through GRADE. Results: Nine studies were included. The follow-up time of treatments varied from 21 days to 6 months. The subgroup meta-analysis showed that the green tea as sachet reduced probing bleeding (SMD = -0.71; 95%CI) and the gingival index (SMD = -0.78; 95%CI) compared to SRP with very low certainty of evidence. The sachet (SMD = -0.29; 95%CI) and dentifrice (SMD = -1.31; 95%CI) reduced plaque index with very low certainty compared to the control. All forms of application of green tea showed very low certainty of evidence (SMD = -0.27; 95% CI) in reducing the probing depth, as well as for the loss of clinical insertion (SMD = -0.42; 95% CI) with low certainty of evidence. Conclusion: There was not a difference in the effectiveness of green tea isolated or in combination with SRP to reduce probing depth. Green tea adjunct to periodontal therapy showed very low certainty of effectiveness for the treatment of periodontal disease.