Pro-abortion advocates claim contraceptives cannot be abortifacients when they prevent implantation, because they changed the definition of pregnancy in 1965 to coincide with implantation, which occurs 6-12 days after fertilization (the beginning of a new human being).
Hormonal contraceptives can work through three mechanisms of action: stopping ovulation, thickening cervical mucus, and thinning the uterine lining to prevent implantation. However, some contraceptives may not employ all three mechanisms.
Emergency contraceptives, hormonal contraception, and IUDs may, in varying degrees, act as abortifacients. It depends on their mechanisms of action, and there are still unknowns in some cases.