A 22-year-old woman consults you for treatment of hirsutism. She is obese and has facial acne and hirsutism on her face and periareolar regions and a male escutcheon. Serum LH level is 35 mIU/mL and FSH is 9 mIU/mL. Androstenedione and testosterone levels are mildly elevated, but serum DHAS is normal. The patient does not wish to conceive at this time. Which of the following single agents is the most appropriate treatment of her condition?