When should one use a progesterone only birth control pill?

To avoid estrogen: Most birth control pills also contain estrogen but estrogen can decrease breast milk (for breast-feeding moms), increase blood pressure (for women who already have high blood pressure), cause an increased risk of stroke in women over age 35 who smoke, increase the risk of blood clots in women who have already had a serious blood clot, and aggravate headaches (for women with migraines. ).