What are progestin-only oral contraceptives?

Updated: Oct 16, 2019
  • Author: Frances E Casey, MD, MPH; Chief Editor: Richard Scott Lucidi, MD, FACOG  more...
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Answer

Answer

Progestin-only oral contraceptives, also known as minipills, are not used widely in the United States. Less than 1% of users of oral contraceptives use them as their sole method of contraception. Candidates for use include women who are breastfeeding and women with contraindications to estrogen use. Several formulations are available. One formulation contains 75 mcg of norgestrel. Another has 350 mcg of norethindrone. Drospirenone 4 mg was approved as a progestin-only oral contraceptive in 2019.

Prevention of conception involves a combination of mechanisms similar to, but not as efficacious as, combination oral contraceptives. Mechanisms of action include (1) suppression of ovulation (not uniformly in all cycles); (2) a variable dampening effect on the midcycle peaks of LH and FSH; (3) an increase in cervical mucus viscosity by a reduction in its volume and an alteration of its structure; (4) a reduction in the number and size of endometrial glands, leading to an atrophic endometrium not suitable for ovum implantation; and (5) a reduction in cilia motility in the fallopian tube, thus slowing the rate of ovum transport.


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