Chapter 31  ·  Module 2
Hormonal Contraception
Mechanisms · Methods · Emergency Contraception · Contraindications
Combined Oral Contraceptive Mechanism Hierarchy
Primary (99%+ cycles)
Anovulation
  • Sustained estrogen + progestin suppresses hypothalamic-pituitary-ovarian axis
  • No luteinizing hormone surge → no ovulation → no egg to fertilize
  • Disrupted by missed pills, vomiting, enzyme inducers
Secondary
Cervical Mucus Thickening
  • Progestin converts mucus to viscous, impermeable state
  • Blocks sperm penetration
  • Primary mechanism of norethindrone minipill
  • Norethindrone: 3-hour dosing window — permeability returns by hour 4
Tertiary Backup
Endometrial Atrophy
  • Thin, poorly vascularized endometrium
  • Unsuitable for implantation
  • Operates only if mechanisms 1 and 2 fail
  • Not a primary contraceptive mechanism
Progestin-Only Methods Compared
Method Primary Mechanism Duration Key Advantage Key Counseling Point
Norethindrone minipill 0.35 mg Cervical mucus thickening Daily (3-hr window) No estrogen 3-hour dosing window — strictest of all methods
Desogestrel minipill 75 mcg Ovulation suppression + mucus Daily (12-hr window) Ovulation suppression without estrogen More forgiving missed-pill window than norethindrone
Etonogestrel implant (Nexplanon) Ovulation suppression 3 years Most effective reversible contraceptive Irregular bleeding common (year 1); fertility returns in 3–4 weeks
Depot medroxyprogesterone acetate Ovulation suppression 12 weeks per injection Large depot buffer vs. drug interactions Fertility delay: average 9–10 months after last injection
Levonorgestrel intrauterine device (52 mg) Local endometrial + mucus 5–8 years Minimal systemic progestin; preferred with enzyme-inducing drugs Not affected by systemic drug interactions
Emergency Contraception Comparison
72-Hour Window
Levonorgestrel 1.5 mg
  • Inhibits/delays luteinizing hormone surge (pre-ovulatory only)
  • No effect after ovulation
  • Efficacy reduced at body mass index above 26 kg/m²
  • Substantially impaired at body mass index above 35 kg/m²
  • Over-the-counter availability
120-Hour Window (5 Days)
Ulipristal Acetate 30 mg
  • Progesterone receptor modulator
  • Can inhibit ovulation even after luteinizing hormone surge begins
  • Superior to levonorgestrel at all time points, especially after 72 hours
  • Less weight-dependent than levonorgestrel
  • Interaction: avoid within 5 days of progestin-containing methods
Most Effective — 5-Day Window
Copper Intrauterine Device
  • Copper ions toxic to sperm → prevents fertilization
  • Failure rate below 0.1% — most effective EC available
  • Not weight-dependent
  • No drug interactions
  • Provides ongoing contraception for up to 10 years
  • Preferred if currently on any hormonal method
Contraindications — Combined vs. Progestin-Only
Condition Combined Hormonal Progestin-Only Note
Prior VTE or thrombophilia Category 4 (absolute CI) Category 2 (safe) Ethinyl estradiol amplifies clotting risk
Migraine with aura Category 4 (absolute CI) Category 2 (safe) Ethinyl estradiol multiplies stroke risk
Severe hypertension Category 4 (absolute CI) Category 2–3 Controlled hypertension: Category 3 for combined
Age over 35, heavy smoking Category 4 (absolute CI) Category 2 (safe) Arterial thrombotic risk synergy
Active liver disease Category 4 (absolute CI) Category 3 Ethinyl estradiol stimulates compromised liver
Current breast cancer Category 4 (absolute CI) Category 4 (absolute CI) Exception: ALL hormonal methods contraindicated
Core Rule — Progestin-Only Safety Advantage

Most conditions that make combined hormonal methods Category 3 or 4 are Category 1 or 2 for progestin-only methods — because the risk arises from ethinyl estradiol, not from progestin. The single exception: current breast cancer is Category 4 for ALL hormonal methods.