Are intrauterine devices (IUDs) and subdermal birth controls, such as Nexplanon (etonogestrel), combined contraceptives or progesterone-only?

IUDs and Subdermal Birth Controls are Progestin-Only Contraceptives

Intrauterine devices (IUDs) and subdermal birth controls such as Nexplanon (etonogestrel) are progestin-only contraceptives, not combined contraceptives. 1

Types of Contraceptives

Progestin-Only Methods:

• Intrauterine Devices (IUDs):

  • Levonorgestrel-releasing IUD (LNG-IUD): Contains only progestin (levonorgestrel) that is released locally within the uterine cavity 1, 2
  • Copper IUD (Cu-IUD): Non-hormonal method that does not contain any hormones 1, 3

• Subdermal Implants:

  • Etonogestrel implant (Nexplanon): Contains only progestin (etonogestrel) 1, 4

• Other Progestin-Only Methods:

  • Progestin-only pills (POPs) 1
  • Depot medroxyprogesterone acetate (DMPA) injections 1, 4

Combined Hormonal Contraceptives (CHCs):

• Contain both estrogen and progestin 1, 5
• Include:
  • Combined oral contraceptives (COCs) 1
  • Combined hormonal patch 1
  • Combined vaginal ring 1, 6

Mechanism of Action

Progestin-Only Methods (IUDs and Implants):

• LNG-IUD works primarily through:

  • Local release of levonorgestrel within the endometrial cavity 2
  • Strong suppression of endometrial growth 2
  • Thickening of cervical mucus to inhibit sperm penetration 5
  • Minimal systemic absorption 3

• Etonogestrel implant (Nexplanon) works through:

  • Inhibition of ovulation 5
  • Thickening of cervical mucus 5
  • Changes to the endometrium that prevent implantation 5

Clinical Considerations

Effectiveness:

• Both IUDs and subdermal implants are highly effective with failure rates of less than 1% per year 1, 4
• They are classified as long-acting reversible contraceptives (LARC) 4
• Their effectiveness is not dependent on user compliance, unlike combined hormonal methods 3, 4

Safety Profile:

• Progestin-only methods like IUDs and implants can be safely used in women with:
  • History of venous thromboembolism 3
  • Cardiovascular disease 1
  • Migraine with aura 1
  • Breastfeeding women 6
  • Smokers over age 35 6

Common Side Effects:

• LNG-IUD may cause:

  • Reduced menstrual bleeding or amenorrhea in 35% of women after 2 years 3, 2
  • Initial irregular spotting in the first 2-3 months 2

• Etonogestrel implant may cause:

  • Changes in bleeding patterns 4
  • Headache 6
  • Mood changes 4

Important Distinctions

• Key difference: Combined contraceptives contain both estrogen and progestin, while IUDs and subdermal implants contain only progestin or no hormones (copper IUD) 1

• The U.S. Medical Eligibility Criteria for Contraceptive Use clearly categorizes these methods separately, with different risk classifications for various medical conditions 1

• Drug interactions differ between combined hormonal contraceptives and progestin-only methods like IUDs and implants 1

Clinical Applications

• For patients with contraindications to estrogen (such as those with positive antiphospholipid antibodies), IUDs and implants are strongly recommended as safe alternatives 1

• For adolescents and women who have never been pregnant, both IUDs and implants are safe and effective options with high continuation rates 1, 4

• For women with medical conditions like SLE, IUDs and progestin implants are preferred over other hormonal contraceptives 1

Remember that while IUDs and subdermal implants are highly effective at preventing pregnancy, they do not protect against sexually transmitted infections 1.