How Do IUDs Work? (Mechanism of Action)


Currently available IUDs work by preventing sperm from fertilizing ova, although some aspects of the precise mechanism of action are not known. IUDs are not abortifacients; they do not interrupt an implanted pregnancy. Pregnancy is prevented by a combination of the ‘foreign body effect’ of the plastic frame and the specific action of the medication (copper or Levonorgestrel) that is released, which impairs sperm function and implantation, and prevents fertilization.[i]


[i] Hatcher RA, Trussell J, Nelson A, Cates Jr., W, Kowal, D, Policar, M, Contraceptive Technology: Twentieth Revised Edition. New York NY: Ardent Media, 2011, pg. 150. 184.