A 24-year-old woman requests combined oral contraceptive pills for dysmenorrhea. She has regular cycles and no contraindications. What is the primary mechanism by which COCPs reduce dysmenorrhea?

• A Direct analgesic effect on uterine nerve endings
• B Suppression of ovulation and reduction of endometrial prostaglandin production ✓
• C Thinning of the myometrial layer reducing contractility
• D Increased endometrial blood flow reducing ischemia

Explanation

COCPs suppress ovulation and endometrial proliferation, resulting in a thinner endometrium that produces significantly less prostaglandin F2α and prostaglandin E2 during menstruation. Reduced prostaglandins mean reduced uterine cramping and pain. Option A is incorrect as COCPs have no direct analgesic action. Option C is wrong as the myometrium is not thinned. Option D is the opposite of the effect.

Reference: Williams Gynecology, 4th ed.

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