Progestins

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Summary

Progestins are drugs used to mimic the hormone’s progesterone’s effects in the body.  They function by activating progesterone receptors in the uterus, which helps to maintain the endometrial lining. There are different progestins used as drugs, including levonorgestrel, medroxyprogesterone, etonogestrel, megestrol and norethindrone. Progestins are often used clinically for contraception by preventing ovulation and thickening cervical mucus. They can also be used to reduce endometrial growth. While oral contraceptive pills that include progestins can cause clots, it's worth noting that the clot risk is a result of estrogen and not progestin in the pill. Lastly, a progestin withdrawal challenge may be used to help identify the diagnosis in abnormal menses or uterine bleeding.

Key Points

  • Progestins
    • Medications
      • Levonorgestrel
        • Found in OCPs and IUDs
      • Medroxyprogesterone
        • Found in OCPs or depot injections
      • Norethindrone
        • Found in OCPs
      • Etonogestrel
        • found in vaginal rings and implants
      • Megestrol
    • Mechanism
      • Synthetic progesterone agonists
        • Binds progesterone receptors on the uterus and hypothalamus
    • Indications
      • Contraception
        • Anovulation
          • in oral contraceptives/patch/depot injections
          • Synthetic progestins act on the hypothalamus to induce negative feedback→ decreased GnRH → decreased LH/FSH → decreased LH surge → no ovulation
        • Thickens cervical mucus
          • in IUDs/progestin-only pills
          • Limits the sperm access to ova
        • Thinning of uterine lining
          • All progesterones therefore impair embryo implantation
          • This is a minor effect in comparison to the above
      • Reduces growth of endometrial tissue
      • Used in the treatment of endometrial hyperplasia/cancer and endometriosis
        • Increases endometrial vascularity and shedding for menses
        • Counteracts endometrial growth/hyperplasia induced by estrogens in combined OCPs
      • Progestin challenge for abnormal uterine bleeding
        • presence of withdrawal bleeding excludes anatomic defects (i.e. Asherman syndrome) and chronic anovulation without estrogen
    • Adverse Effects
      • PE/DVT and other hypercoagulable events seen in combined progestin/estrogen OCPs
        • Due to estrogen, not progesterone in formulation; Used alone, progestins have NOT been associated with thromboembolic events.
      • Decreased bone density (osteoporosis)