The estrogen component of COCs can cause breast fullness and tenderness. Although the fullness often remains as long as COCs are taken, the tenderness usually resolves after a few months of use. If the tenderness persists, one should consider switching the patient to a COC containing a lower dose of estrogen.

The incidence of benign breast disease (fibrocystic changes and fibroadenomas) is decreased among women who have used high-dose COCs for more than 2 years.43 Women using high-dose COCs for more than 6 years have an approximately 50% reduction in benign breast disease. Low-dose COCs may have an attenuated benefit.

The quantity and quality of milk produced during lactation have been found to be decreased with COC use.44 Similarly, women using COCs have been found to breast-feed for shorter lengths of time postpartum. Both estrogens and progestins are secreted in the milk, and although these steroids decrease the levels of both proteins and fats in human milk, no adverse effects on the growth or development of infants have been identified.45 Although COC use during lactation is not harmful to infants, it is not recommended because it makes breast-feeding more difficult.

LN implants (Norplant) have been associated with breast tenderness in 11% of users in a
large U.S. study.46 The tenderness may be due to temporarily elevated follicular estradiol levels in women with lower LN serum concentrations and usually resolves over time. After excluding pregnancy as a possible cause of the mastalgia, reassurance is usually all that is necessary. POPs and DMPA are rarely associated with breast complaints.

For many years a great deal of controversy surrounded the issue of breast cancer risk in COC users. Some epidemiologic studies have shown no increased risk of breast cancer with COC use,47,48 and 49 whereas others have shown an increased risk of breast cancer in women using COCs before the age of 25 years.50,51,52 and 53