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.