This study aims to compare two treatment plans for adults with bladder pain syndrome (also called interstitial cystitis), a disease that causes long-lasting bladder pain, frequent urination and urgent need to pee. All participants will receive standardized patient education and behavioral training to relieve urinary discomfort. Half of the participants will only get this behavioral intervention, while the other half will take oral venlafaxine in addition to the same behavioral training for 12 weeks. We will check patients' pain levels, urination frequency, sleep quality, mood and daily life ability at 1, 2, 6 and 12 weeks of treatment. The main goal is to see whether adding venlafaxine can better ease bladder pain and urinary symptoms without obvious side effects. This research will provide safer and more effective treatment suggestions for patients with bladder pain syndrome.

Inclusion Criteria:

Age ≥ 18 years (all genders) Confirmed IC/BPS diagnosis fulfilling AUA 2015 and ESSIC standardized diagnostic criteria, ruled out confounding urologic disorders Predominant lower urinary tract symptoms present for most days in the past 3 months Baseline bladder/pelvic pain and urinary frequency score ≥ 3 points on 0-10 Likert scale within prior 4 weeks

Exclusion Criteria:

Symptomatic urethral stricture Active degenerative/inflammatory neurological disease altering bladder/intestinal function Uncontrolled active autoimmune disease or systemic infection Medical history of pelvic tuberculosis, pelvic radiotherapy or chemotherapy-induced cystitis History of non-cutaneous malignant tumors Current diagnosis of severe psychiatric disorders (major depressive disorder, bipolar disorder, schizophrenia, psychotic disorders) Clinically significant moderate-severe cardiac, pulmonary, hepatic or renal insufficiency Documented hypersensitivity to venlafaxine or other SNRI drugs Concurrent regular use of antibiotics or NSAIDs throughout trial period Pregnancy or breastfeeding state at screening

The plan for sharing individual participant data (IPD) has not yet been finalized. After trial completion, the research team will evaluate data sharing feasibility under the supervision of the Institutional Review Board, including assessment of participant privacy protection, data de-identification procedures, institutional data management policies and relevant domestic clinical research data regulations. A formal data sharing plan will be formulated and updated to this registry before study results publication.