Objective To evaluate the efficacy of boric acid as an adjunct to non-surgical periodontal therapy, in comparison with a placebo adjunct, in terms of changes in probing pocket depth (PPD) and clinical attachment level (CAL), in patients with periodontitis. Methods Four electronic databases were searched from inception to May 2020 (PubMed, Cochrane CENTRAL, EMBASE via OVID and Web of Science). Clinical outcomes were extracted, pooled and meta-analyses conducted using mean difference with standard deviations. Results For PPD, a mean additional reduction of 0.58 mm (95% CI: -0.03-1.19 mm, p = 0.06) was observed at 3 months and a mean additional reduction of 1.18 mm (95% CI: 0.97-1.40 mm, p < 0.05) at 6 months, compared with placebo. For CAL, a mean additional gain of 0.62 mm (95% CI: -0.07-1.32 mm, p = 0.08) was observed at 3 months and a mean additional gain of 1.24 mm (95% CI: 0.89-1.58 mm, p < 0.05) at 6 months, compared with placebo. No adverse events were reported in any studies. Conclusions The adjunctive use of boric acid in non-surgical periodontal therapy results in improved treatment outcomes at 3 and 6 months, with no adverse events reported.