During breastfeeding, progestin-only pills are highly effective, complementing the natural protection that breastfeeding offers. They do not decrease milk production. For example, by reducing menstrual bleeding, OCs help prevent iron deficiency anemia, which is common and often serious in developing countries. OC use halves the risk of cancers of the uterine lining and of the ovary. Some protection persists for many years after OC use stops.
Some evidence suggests that OCs reduce risk of colorectal cancer, too.
Research has better defined which women would face appreciable risk of heart attack or stroke if they used OCs women over age 35 who smoke or who have high blood pressure. For all other women, using OCs is clearly safer than childbearing in both developing and developed countries. Resolving Uncertainties Even some of the most persistent uncertainties concerning OCs are now coming into perspective. Research suggests that OCs may somewhat speed up the diagnosis of already existing breast cancers perhaps because tumors are more readily detected, tumor growth is accelerated, or both. OC use does not increase lifetime risk of developing breast cancer.