Good question about birth control pills and estrogen exposure

Q. I had a question about the increased estrogen exposure and increased risk for breast and endometrial cancer. Is birth control an increased estrogen exposure? Or does it simulate the hormones of being pregnant? Or something completely different.

A. Good question! No, birth control pills do not expose you to excess estrogen. In fact, they may actually decrease your overall estrogen exposure. 

There are many different types of oral contraceptive pills (OCPs) – but basically they boil down to two formulations: they either contain a combination of estrogen and progesterone, or they just contain progesterone. They prevent pregnancy by preventing follicle maturation and ovulation.

Here’s how they work. Progesterone inhibits the release of GnRH from the hypothalamus – which means that you’ll release less FSH and LH from your pituitary, which means that both follicular maturation (controlled by FSH) and ovulation (controlled by LH) are inhibited. This means that you’re also making less estrogen (follicles make estrogen as they develop; that’s what actually triggers the LH surge that leads to ovulation).

Estrogen has an inhibitory effect on FSH release – so that’s why some OCPs also have a little estrogen in them. But that little bit of estrogen in the pill doesn’t increase your overall estrogen exposure, because at the same time, you’re inhibiting your own estrogen production (by the follicles) – so the net effect is an estrogen deficit.

So that’s why OCPs don’t increase the risk of developing estrogen-related cancers like breast and endometrial cancer. In fact, they may even be protective against some cancers (ovarian cancer in particular), although this hasn’t been definitively proven yet. 

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