Can birth control pills cause breast enlargement?

Some can: The hormones in certain oral contraceptives can indeed increase breast size in some individuals. No real way to know ahead of time if you are going to be one of the people that this happens to.

Breast size: Oral contraceptives don't cause breast enlargement.

Progesterone only: Birth control pills that only contain progesterone derivatives are least likely to cause breast enlargement, because the estrogen that stimulates breast tissue is missing.