Background: Bladder pain syndrome (BPS) is a chronic condition characterized by pelvic pain and lower urinary tract symptoms. Pentosan polysulfate sodium (PPS) is the only oral therapy licensed in the United Kingdom (UK) for BPS; however, evidence on its effectiveness is inconsistent, with limited data for off-label use in ketamine- or radiation-induced cystitis. Objective: This study evaluates real-world outcomes of PPS in patients with BPS and other chronic bladder pain at a UK tertiary center. Methods: A retrospective review included 42 patients prescribed PPS between 2020 and 2024 for BPS (n = 29), ketamine-induced cystitis (n = 9), or radiation/chemotherapy-induced cystitis (n = 4), excluding Bacillus Calmette–Guérin cystitis. Demographics, comorbidities, prior treatments, symptom severity, and treatment response were recorded. Changes in quality of life (QoL) and Interstitial Cystitis Symptom Index/Interstitial Cystitis Problem Index (ICSI/ICPI) scores were analyzed using the Wilcoxon signed-rank test and one-way analysis of variance. Results: The mean age was 49.7 years, and 81% were female, with a median follow-up of 15.3 months. All patients were severely symptomatic at baseline. Among those with follow-up data, 42.5% were asymptomatic, 25% mildly symptomatic, and 32.5% remained severely symptomatic. QoL improved significantly (Wilcoxon Z = −4.71, p<0.001). Greatest reductions in ICSI and ICPI scores were observed in BPS patients, with modest improvements in off-label groups. Side effects occurred in 14.2% of patients. PPS was associated with significant symptom improvement and acceptable tolerability in a treatment-refractory cohort, particularly in BPS. Conclusion: Modest benefits in ketamine- and radiation-induced cystitis suggest potential off-label utility, warranting further investigation. These findings support PPS use in selected cases, while accounting for placebo effects and disease heterogeneity.