Progestin-only contraceptives: this is the method of hormonal birth control recommended by acog for breastfeeding women. This includes "minipills" and depo-provera. Progestin-only contraceptives are not thought to affect the quality of breast milk -- in fact, they may slightly increase the volume of milk while breastfeeding compared with nonhormonal methods. Because it may have some effect on breast milk, lactating women should not begin taking these contraceptives prior to two or three weeks postpartum.
Combination estrogen-progestin contraceptives: any contraceptives containing estrogen have been shown to reduce the quantity and quality of breast milk. The world health organization recommends that the breastfeeding woman wait at least six months after childbirth to start using these pills. And their labels, written by the food and drug administration, currently read, "if possible, the nursing mother should be advised not to use oral contraceptives but to use other forms of contraception until she has completely weaned her child." but it can be argued that these warnings are a result of earlier studies, when combination pills used higher doses of estrogen. The lower-dose tablets used today probably have less effect on the quality and quantity of breast milk. As a result, there is no definitive answer regarding if and how much a combination pill taken today may affect breast milk.
My doctor put me on depo-provera at my 6 week post-partum. It's been great at preventing pregnancy (it's the only protection my husband and I have used in 5 1/2 years). But the side effects can be horrible for some people so think it over clearly and discuss it with your doctor. There are also low hormone pills out now (like ortho-tricyclen low) that you *may* be able to use (not positive on that one). Just ask your doc about it. He/she will know what you can use :d
