A 32-year-old woman complains of heavy menstrual bleeding, with periods lasting 8 days and requiring pad/tampon changes every 1-2 hours on the heaviest days, causing significant disruption to her life. She is otherwise well. Examination is normal. Full blood count shows Hb 108 g/L (mild anaemia). According to NICE NG88, what is the recommended first-line pharmacological treatment, assuming no fibroids >3cm or suspected significant pathology?