A 48-year-old woman presents with a 6-month history of menorrhagia (heavy menstrual bleeding), with clots and flooding. She has no intermenstrual or postcoital bleeding. A pelvic examination is normal. Full blood count shows Hb 10.5 g/dL, MCV 78 fL. According to NICE NG88, after initial assessment and exclusion of structural or histological abnormalities (e.g. via ultrasound if indicated), what is the first-line pharmacological treatment if contraception is not desired?