A 28-year-old woman presents to her GP with concerns about her menstrual periods. She reports heavy menstrual bleeding (HMB) for the past year, soaking through super-plus tampons every 2 hours on her heaviest days and passing large clots. This is impacting her quality of life. She is otherwise well. Examination is unremarkable. A FBC is normal. What is the most appropriate first-line pharmacological treatment to offer for HMB, assuming no identified pathology and contraception is not a priority?