The mechanism of action of<unk> -only contraceptives depends on the<unk>  activity and dose. * Very-low-dose<unk> -only contraceptives, such as traditional<unk> s (and subdermal implants Norplant and Jadelle and intrauterine systems Progestasert and Mirena), inconsistently inhibit ovulation in ~50% of cycles and rely mainly on their<unk> ic effect of thickening the cervical mucus, thereby reducing sperm viability and penetration. * Intermediate-dose<unk> -only contraceptives, such as the<unk>  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<unk> s. * High-dose<unk> -only contraceptives, such as the injectables Depo-Provera and Noristerat, completely inhibit follicular development and ovulation. The same cervical mucus changes occur as with very-low-dose and intermediate-dose<unk> s. In anovulatory cycles using<unk> -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).
Progestogen-only pill
Extended cycle combined hormonal contraceptive
Progestogen-only injectable contraceptive
Progestogen-only contraception
Estradiol-containing birth control pill
High-dose estrogen
Levonorgestrel-releasing implant
Male contraceptive