Eli5 How do birth control pills not cause a build up in uterus lining

Question

In a normal period, the uterus lining is thickened and then shed during the period.

What happens to the lining when using birth control pills? If it’s not shed does it not just keep on getting thicker and thicker?

In: 13

Answer 1

When you take a 28 day cycle of BC, it’s 21 days on (hormones) 7 off (placebo) so you still have a period as you normally would. That would include shedding the uterine lining once a month.

If you’re not having periods at all, I’d suggest a Dr
visit.

ETA:I’m old, so. Obviously I have some reading up to do. Thanks to all that responded.