Synthroid thyroid replacement hormone just replaces what the body isn't making naturally. I have taken it for years and nursed all 3 kids. Kathleen Kathleen B. Bruce, BSN, IBCLC, LLLeader, co-owner Lactnet, LLLOL, Corgi-L LACTNET WWW site: http://www.mcs.com/~auerbach/lactation.html Personal WWW page: http://www.together.net/~kbruce/kbbhome.html