Breast tenderness is relatively common during the first month of BCPs and less common thereafter.

When this occurs, it is because the women are still making their own hormones (the BCPs have not yet suppressed ovarian function), and in addition, they are getting extra estrogen from the pill.

Persistent breast tenderness is usually because of continued failure of the BCPs to suppress ovarian function, resulting in the combination of the woman’s own hormones, plus the pill hormones. The breasts, being particularly sensitive to higher levels of estrogen, respond with tenderness, sensitivity, and sometimes breast enlargement.

This can be particularly troublesome among women with pre-existing fibrocystic breast changes. Women with fibrocystic breasts usually notice the breast tenderness and nodularity becoming worse just before menses and much better after the onset of flow. BCPs are usually an effective treatment for fibrocystic breasts because the accompanying suppresion of ovarian function (with the add-back estrogen in the pill) leads to lower and more stable levels of estrogen in the blood stream. Because of the expected improvement in fibrocystic disease among women taking BCPs, a subsequent development of significant breast pain should be viewed as unusual. It may be due to the particular pill being insufficiently strong to consistently suppress ovarian function. In this case, changing to a BCP with a stronger progestin and a longer half life should resolve the problem.

A careful breast exam should be done to rule out newly-developed breast disease. A recent onset of significant breast tenderness should raise your suspicions about a possible unsuspected pregnancy.