Background: Intravesical bacillus Calmette–Guérin (BCG) is the standard adjuvant treatment for intermediate- and high-risk non– muscle-invasive bladder cancer (NMIBC). This study evaluated the efficacy and safety of BCG using a PRISMA-2020–compliant metaanalysis.

Methods: Randomized controlled trials comparing intravesical BCG with transurethral resection alone or intravesical chemotherapy were identified from PubMed, Embase, and Cochrane databases. Primary outcomes were tumour recurrence and disease progression. Secondary outcomes included cancer-specific mortality and treatment-related toxicity. Random-effects models were used.

Results: Thirty-two studies involving 11,421 patients were included. BCG significantly reduced tumour recurrence (RR 0.61, 95% CI 0.55–0.68) and disease progression (HR 0.73, 95% CI 0.61–0.87). Maintenance therapy improved recurrence-free survival compared with induction alone. Reduced-dose regimens demonstrated comparable efficacy with lower toxicity.

Conclusions: Intravesical BCG remains the most effective adjuvant therapy for NMIBC. Maintenance therapy is essential for optimal outcomes, while dose optimization may improve tolerability without compromising efficacy.