Progestin-only pills are safe and effective contraceptives for breastfeeding women because they do not affect milk production, unlike estrogen-containing pills which can reduce milk supply. They are suitable immediately postpartum and have a lower risk of thrombosis. This makes them ideal for women who are breastfeeding and wish to avoid estrogen-related side effects. The primary benefit is maintaining lactation while providing contraception.

Reference: Contraceptive Technology, Robert A. Hatcher, 21st Edition.