Mechanism of Action
The mechanism of action of progestogen-only contraceptives depends on the progestogen activity and dose.
- Very-low-dose progestogen-only contraceptives, such as traditional progestogen-only pills (and subdermal implants Norplant and Jadelle and intrauterine systems Progestasert and Mirena), inconsistently inhibit ovulation in ~50% of cycles and rely mainly on their progestogenic effect of thickening the cervical mucus, thereby reducing sperm viability and penetration.
- Intermediate-dose progestogen-only contraceptives, such as the progestogen-only pill Cerazette (or the subdermal implant Nexplanon), allow some follicular development (part of the steps of ovulation) but much more consistently inhibit ovulation in 97–99% of cycles. The same cervical mucus changes occur as with very-low-dose progestogens.
- High-dose progestogen-only contraceptives, such as the injectables Depo-Provera and Noristerat, completely inhibit follicular development (see above) and ovulation. The same cervical mucus changes occur as with very-low-dose and intermediate-dose progestogens.
In anovulatory cycles using progestogen-only contraceptives, the endometrium is thin and atrophic. If the endometrium were also thin and atrophic during an ovulatory cycle, this could, in theory, interfere with implantation of a blastocyst (embryo).
Read more about this topic: Progestogen-only Pill
Famous quotes containing the words mechanism of, mechanism and/or action:
“Life is an offensive, directed against the repetitious mechanism of the Universe.”
—Alfred North Whitehead (1861–1947)
“Life is an offensive, directed against the repetitious mechanism of the Universe.”
—Alfred North Whitehead (1861–1947)
“These people who are always briskly doing something and as busy as waltzing mice, they have little, sharp, staccato ideas.... But they have no slow, big ideas. And the fewer consoling, noble, shining, free, jovial, magnanimous ideas that come, the more nervously and desperately they rush and run from office to office and up and downstairs, thinking by action at last to make life have some warmth and meaning.”
—Brenda Ueland (1891–1985)