A 29-year-old woman presents with heavy menstrual bleeding, reporting soaking through pads every 1-2 hours on her heaviest days and passing large clots. She feels tired all the time. Her periods are regular. Examination is unremarkable. Full blood count confirms iron deficiency anaemia (Hb 95 g/L). According to NICE NG88, after excluding structural or histological abnormalities (assuming initial assessment/examination is normal), what is a suitable first-line pharmacological treatment option to reduce bleeding?