Progesterone is a hormone created in the ovaries and adrenal glands. During pregnancy, it hinders ovulation and stops menstruation, allowing the embryo to attach to the uterine wall and grow. Many doctors recommend progesterone-only birth control pills, also called mini-pills, to breastfeeding women because they do not affect the milk supply as much as combination birth control pills made from progesterone and estrogen. However, progesterone pills can still affect breastfeeding.
Milk Decrease
A study conducted in 1984 by the World Health Organization found that progesterone-only pills decreased the milk supply of some women by 12 percent. This is less than the 30 percent to 50 percent decrease combination pills can cause.
Increased MIlk Supply
Progesterone pills have also been known to increase the milk supply of some women. Doctors at Siriraj Hospital in Bankok, Thailand, found that women who took progesterone-only pills produced more milk than other women. However, this is not a common effect and mostly occurs in women with lower natural progesterone.
Increased Risk of Diabetes
Mini-pills can increase a breastfeeding woman's risk of developing type 2 diabetes if she had gestational diabetes. A study by the University of Southern California School of Medicine found that these women are three times more likely to develop diabetes when taking progesterone pills than breastfeeding women who use other forms of birth control.
Milk Composition Changes
Progesterone pills can lower the amounts of protein, nitrogen and lactose in breast milk. These effects are only seen in doses larger than a single pill, but for this reason, doctors warn against double dosing if you miss a pill.
