14.3 Progestin-Only Methods & Emergency Contraception
Key Takeaways
- Norethindrone progestin-only pills require dosing within a 3-hour window with 48 hours of backup if late, while drospirenone allows a 24-hour window.
- Depot medroxyprogesterone is given every 13 weeks with a 2-week grace period, and return of fertility averages 9 to 10 months after the last injection.
- The copper IUD is the most effective emergency contraception, exceeding 99 percent, and can be placed up to 5 days after intercourse or ovulation.
- Ulipristal acetate is more effective than levonorgestrel, especially closer to ovulation and at higher body weight, and works up to 120 hours.
- Progestin-containing contraception must not be started for 5 days after ulipristal, because progestin blunts the selective progesterone receptor modulator effect.
Last updated: September 2026
Progestin-Only Pills (POPs) & Injectable Contraception
Progestin-only contraceptives provide safe, highly effective alternatives for individuals with medical contraindications to estrogen (e.g., smokers aged ≥35, hypertension, migraine with aura, thromboembolic history).
1. Progestin-Only Pills (POPs)
- Traditional Norethindrone (0.35 mg daily):
- Mechanism: Thickens cervical mucus within 2 to 4 hours of ingestion (forming an impassable barrier to sperm) and causes endometrial thinning. It does NOT reliably suppress ovulation (ovulation occurs in ~50% of cycles).
- The Strict 3-Hour Window: The cervical mucus thickening effect wanes significantly after 22 to 24 hours. If a dose is delayed by more than 3 hours (>27 hours since last dose): take the missed pill immediately, take the next pill at the regular time, and use back-up barrier contraception for 48 hours.
- Drospirenone (Slynd: 4 mg daily, 24 active / 4 inert):
- Mechanism: Reliably suppresses ovulation; allows a 24-hour missed pill window (identical flexibility to COCs). Demonstrates mild anti-mineralocorticoid activity (monitor serum potassium if co-administered with ACE inhibitors, ARBs, or potassium-sparing diuretics).
2. Depot Medroxyprogesterone Acetate (DMPA / Depo-Provera)
- Dosing & Administration: 150 mg intramuscularly (deltoid or ventrogluteal muscle) or 104 mg subcutaneously every 13 weeks. The CDC allows a grace period of up to 15 weeks from the last injection without requiring additional contraceptive precautions or pregnancy exclusion.
- Mechanism of Action: High-dose systemic progestin exerts potent negative feedback on the HPO axis, suppressing GnRH and the mid-cycle LH surge to reliably abolish ovulation. Induces marked endometrial atrophy and cervical mucus thickening.
- Clinical Benefits: High efficacy (typical failure rate 4%); amenorrhea in 50% by 1 year and 70% by 2 years; marked reduction in dysmenorrhea; reduces endometrial cancer risk by 80%; decreases vaso-occlusive crises in patients with sickle cell disease; reduces epileptic seizure frequency.
- Bone Mineral Density (BMD) Loss & ACOG/CDC Guidance: The FDA Black Box Warning notes loss of BMD with prolonged use due to hypoestrogenism. However, extensive clinical trials confirm that bone mineral density loss is substantially or completely reversible after discontinuation, returning to baseline levels. Both ACOG and the CDC state that DMPA use should NOT be restricted to 2 years, and routine monitoring of BMD with DEXA scans is strictly not recommended.
- Delayed Return of Fertility: Ovulatory suppression persists beyond the 13-week interval; the median time to conception following DMPA discontinuation is 9 to 18 months (average ~10 months). Crucial anticipatory counseling for patients desiring pregnancy in the near future.
Emergency Contraception (EC)
Emergency contraception prevents pregnancy following unprotected intercourse, sexual assault, or contraceptive failure (e.g., condom rupture, missed oral pills, dislodged diaphragm).
Emergency Contraception Options & Clinical Selection
├── 1. Intrauterine Devices (Most Effective EC - Failure Rate <0.1%)
│ ├── Copper IUD (ParaGard) ──> Insert up to 120 Hours (5 Days) post-coitus
│ └── 52 mg Levonorgestrel IUD (Mirena/Liletta) ──> Insert up to 120 Hours post-coitus
│ └── Provides immediate, continuous top-tier LARC contraception for 8-12 years
├── 2. Ulipristal Acetate (Ella 30 mg Oral - Preferred Oral EC in BMI >30 kg/m²)
│ ├── Selective Progesterone Receptor Modulator (SPRM) ──> Effective up to 120 Hours
│ ├── Delays follicular rupture even AFTER the LH surge has started to rise
│ └── DRUG INTERACTION: Delay starting regular hormonal contraception for 5 DAYS
├── 3. Levonorgestrel (Plan B One-Step 1.5 mg Oral - Best within 72 Hours)
│ ├── Over-the-counter without age/prescription restrictions ──> Effective up to 72 Hours
│ ├── Ineffective once LH surge has begun; reduced efficacy if BMI >25-30 kg/m²
│ └── Start regular hormonal contraception immediately ("Quick Start") + 7-day backup
└── 4. Yuzpe Method (Combined Estrogen-Progestin Pills - Lowest Efficacy / Nausea)
└── 100 mcg Ethinyl Estradiol + 0.5 mg Levonorgestrel repeated in 12 hours
Clinical Comparison of Emergency Contraceptive Regimens
| Regimen | Timing Window | Mechanism of Action | Efficacy & Weight Limitations | Immediate Contraceptive Initiation Rule |
|---|---|---|---|---|
| Copper IUD (ParaGard) | Up to 120 hours (5 days) post-coitus | Direct spermicidal action; prevents fertilization | >99.9% effective; efficacy unaffected by patient BMI or body weight | Remains in place; provides immediate ongoing Tier 1 contraception for 10–12 years. |
| 52 mg LNG-IUD (Mirena / Liletta) | Up to 120 hours (5 days) post-coitus | Endometrial decidualization, cervical mucus thickening | Non-inferior to Copper IUD for EC; unaffected by body weight | Remains in place; provides immediate ongoing Tier 1 contraception for 8 years. |
| Ulipristal Acetate (Ella, 30 mg PO) | Up to 120 hours (5 days) post-coitus | Delays or inhibits ovulation; effective even during the early LH surge up to the LH peak | Higher efficacy than oral LNG between 72–120 hours; superior efficacy in individuals with BMI >30 kg/m² (or weight >75 kg / 165 lbs) | Must WAIT 5 DAYS before starting progestin-containing birth control (progestins impair Ella's antiprogestin action); use barrier backup for 14 days. |
| Levonorgestrel (Plan B One-Step, 1.5 mg PO) | Up to 72 hours (marginal efficacy 72–120h) | Delays LH surge prior to onset; ineffective once LH surge begins | High efficacy if taken early; efficacy drops significantly when BMI exceeds 25 kg/m² (ineffective in BMI >30 kg/m²) | Start regular hormonal contraception immediately on the same day ("Quick Start"); use barrier backup for 7 days. |
| Yuzpe Regimen | Up to 72 hours | High-dose estrogen/progestin delays ovulation | Lowest efficacy (~75%); high incidence of severe nausea (50%) and emesis (20%) | Used only when dedicated EC is inaccessible; co-prescribe oral antiemetic (meclizine or ondansetron). |
Test Your Knowledge
A 26-year-old nulliparous woman presents to the clinic on Monday afternoon requesting emergency contraception. She had unprotected penile-vaginal intercourse on Friday evening (approximately 68 hours ago). Her last normal menstrual period began 12 days ago, and her cycles average 28 days. Her body mass index (BMI) is 33 kg/m² (body weight 92 kg / 203 lbs). She does not wish to have an intrauterine device placed today and prefers an oral medication. Which oral emergency contraceptive regimen is the most effective clinical recommendation for this patient?
A
B
C
D