Mechanism of Action
The mechanism of action of progestin only contraceptives depends on the progestin activity and dose. Intermediate dose progestin-only contraceptives, like Nexplanon or Implanon (and the progestin-only pill Cerazette) allow some follicular development but inhibit ovulation in almost all cycles as the primary mechanism of action. Ovulation was not observed in studies of Implanon in the first two years of use and only rarely in the third year with no pregnancies. A secondary mechanism of action is the progestogenic increase in cervical mucus viscosity which inhibits sperm penetration. Hormonal contraceptives also have effects on the endometrium that theoretically could affect implantation, however no scientific evidence indicates that prevention of implantation actually results from their use.
Read more about this topic: Implanon
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