How do combination oral contraceptives reduce menstrual pain?

Combination oral contraceptives reduce menstrual pain primarily by thinning the endometrial lining. This is significant because a thicker endometrial lining tends to lead to heavier menstrual bleeding and more intense cramps, as it requires greater contraction from the uterus to shed the lining. Thinner endometrial tissue results in less prostaglandin release, which is the hormone responsible for causing the uterine contractions that lead to menstrual pain. Therefore, by decreasing the thickness of the endometrial lining, combination oral contraceptives effectively reduce both the volume of menstrual flow and the associated discomfort from cramps.

Other options suggest mechanisms that do not align with how oral contraceptives function. For instance, increasing the endometrial lining or promoting inflammatory products would likely exacerbate menstrual pain rather than alleviate it, while stating that they are ineffective against uterine contractions misrepresents their impact, as they actually moderate these contractions through hormonal regulation.