PURPOSE: Intravesical BCG (bacille Calmette-Guérin) instillation in patients with non-muscle-invasive bladder cancer decreases the risk for tumor recurrence and progression. After one BCG product was discontinued, a chronic global BCG shortage occurred. We focused on identifying a reduced dose of BCG that could maintain efficacy and reduce adverse effects. MATERIALS AND METHODS: We conducted a comprehensive literature search of PubMed, Embase, the Cochrane Library, CINAHL, Web of Science, and Scopus to identify randomized controlled trials through April 2021. The odds ratios (ORs) and 95% confidence intervals (CIs) for the low and standard doses in nine studies were compared. A low dose was defined as a low volume of BCG compared with the standard BCG dose (Armand Frappier, 120 mg; Connaught, 81 mg; Danish 1331, 120 mg; modified Danish 1331, 120 mg; Tokyo 172, 80 mg). RESULTS: The low-dose group experienced aggravated recurrence (OR, 1.45; 95% CI, 1.09-1.94; p=0.01) but similar progression (OR, 1.11; 95% CI, 0.76-1.62; p=0.59), similar cancer-specific survival (OR, 1.02; 95% CI, 0.60-1.75; p=0.93), similar overall survival (OR, 1.09; 95% CI, 0.76-1.56; p=0.65), favorable adverse effects (OR, 0.41; 95% CI, 0.28-0.62; p<0.0001), and favorable withdrawal (OR, 0.42; 95% CI, 0.25-0.71; p=0.001). CONCLUSIONS: Low-dose BCG had more unfavorable outcomes than did standard-dose BCG in terms of recurrence. Tumor progression, cancer-specific survival, and overall survival were similar between the doses. Low-dose BCG improved adverse effects and withdrawal. In the setting of BCG shortage, low-dose BCG may have strong potential as an alternative.