What is the optimal timing, dosage, contraindications, and alternative options for progesterone‑based emergency contraception (levonorgestrel) after unprotected intercourse?

Levonorgestrel Emergency Contraception: Timing and Optimal Use

Yes, progesterone (levonorgestrel) can and should be taken within 24 hours after unprotected intercourse—in fact, the sooner it is taken, the more effective it is. 1

Optimal Timing for Levonorgestrel

Levonorgestrel should be taken as soon as possible within 72 hours (3 days) of unprotected intercourse, with efficacy highest in the first 24 hours. 2, 1

• The FDA-approved window is 72 hours, but effectiveness decreases significantly after this timeframe, with pregnancy rates increasing at 4-5 days post-intercourse. 2
• When taken in the first 24 hours, levonorgestrel prevents approximately 95% of expected pregnancies. 2
• About 7 out of every 8 women who would have gotten pregnant will not become pregnant when levonorgestrel is used as directed. 1

Standard Dosing

The recommended dose is levonorgestrel 1.5 mg as a single dose. 2, 1

• This can be given as one 1.5 mg pill or two 0.75 mg pills taken simultaneously. 2, 3
• If using the two-pill formulation with doses separated, the second 0.75 mg dose can be taken 12-24 hours after the first without compromising efficacy. 4, 3

When Levonorgestrel Is NOT the Best Choice

For women beyond 72 hours (up to 120 hours), ulipristal acetate (UPA) 30 mg is significantly more effective than levonorgestrel. 2, 5

• UPA shows 65% lower pregnancy risk compared to levonorgestrel in the first 24 hours and maintains effectiveness throughout the full 120-hour window. 2, 6
• Between 72-120 hours, UPA prevents significantly more pregnancies than levonorgestrel. 7

For women weighing >165 pounds (75 kg), UPA is more effective than levonorgestrel regardless of timing. 2, 8

• Levonorgestrel may be less effective in obese women regardless of dose. 2

The Most Effective Option

The copper IUD inserted within 5 days of unprotected intercourse is the most effective emergency contraception method with <1% failure rate. 2, 8

• This option provides both emergency contraception and ongoing contraception after insertion. 8

Clinical Algorithm for Emergency Contraception Selection

Within 72 hours AND normal weight (<165 lbs):

• Levonorgestrel 1.5 mg single dose 2

Within 72 hours BUT weight >165 lbs:

• UPA 30 mg preferred over levonorgestrel 2

Between 72-120 hours (any weight):

• UPA 30 mg is the only effective oral option 2, 8
• Levonorgestrel is NOT recommended due to significantly reduced effectiveness 8

Any timepoint within 5 days (seeking maximum efficacy):

• Copper IUD insertion 2, 8

Contraindications

Do not use levonorgestrel if: 1

• Already pregnant (it will not work and is not indicated)
• Allergic to levonorgestrel or any ingredients

Consult a healthcare provider before use if taking: 1

• Efavirenz (HIV medication)
• Rifampin (tuberculosis treatment)
• Seizure medications (epilepsy drugs)
• These medications may reduce levonorgestrel effectiveness and require alternative emergency contraception 1

Critical Post-Administration Instructions

After taking levonorgestrel: 2, 8

• Resume or start regular contraception immediately
• Use barrier method or abstain for 7 consecutive days after restarting hormonal contraception

After taking UPA: 2, 8

• Any contraceptive method can be started immediately
• However, barrier contraception or abstinence is required for 14 consecutive days (or until next menses)
• This longer backup period is critical and often missed

Follow-Up and Monitoring

Expect your next period at the expected time or within one week. 1

• If your period is delayed beyond 1 week, obtain a pregnancy test. 2, 1
• If you vomit within 2 hours of taking levonorgestrel, contact a healthcare provider to determine if you should repeat the dose. 1
• If you experience severe abdominal pain, seek immediate medical attention for possible ectopic pregnancy. 1

Common Pitfalls to Avoid

Do not delay taking emergency contraception. 1

• Every hour counts—efficacy decreases with time for all oral methods. 2

Do not use levonorgestrel as regular birth control. 1

• It is not as effective as regular contraception methods and is intended only for emergency use. 1

Do not assume levonorgestrel protects against STDs. 1

• It will not protect against HIV or other sexually transmitted infections. 1

Do not forget the backup contraception period after emergency contraception use. 2, 8

• This is especially critical with UPA (14 days vs 7 days for levonorgestrel). 8