Marvelon contains desogestrel and ethinylestradiol, a prescription combined oral contraceptive taken once daily for 21 days followed by a 7-day tablet-free interval. Correct daily use and the missed-pill instructions are essential, and it does not protect against sexually transmitted infections. A clinician must assess suitability, especially smoking, migraine with aura and clot risk; sudden chest pain, breathlessness, one-sided leg swelling, weakness or vision disturbance needs urgent care.