How common is hair loss side effect in women taking elmiron, (pentosan) and will hair loss stop if drug is discontinued?

See answer: In the clinical trials leading to FDA approval of Elmiron (pentosan) for the treatment of Interstitial Cystitis, hair loss (alopecia) was self/reported by 4% of the ~2500 patients who took Elmiron (pentosan) for between 3 and 12 months. In my experience, I would estimate noticeable hair loss by the patient to be slightly higher and nearly always reversible upon stopping the medication.