How should levonorgestrel 1.5 mg be administered for emergency contraception, and what are its contraindications and common side effects?

Levonorgestrel 1.5 mg for Emergency Contraception

Levonorgestrel 1.5 mg should be taken as a single oral tablet as soon as possible within 72 hours (3 days) after unprotected intercourse, though it can be used up to 5 days post-coitus with decreasing effectiveness. 1, 2

Administration

• Single-dose regimen: Take one 1.5 mg tablet orally as soon as possible after unprotected intercourse
• Alternative split-dose regimen: Two 0.75 mg doses taken 12 hours apart (equally effective but less convenient) 3, 4
• Timing is critical: Effectiveness decreases with delay—the sooner taken, the better the outcome 2
• Maximum window: Can be used up to 120 hours (5 days) after intercourse, though efficacy is highest within 72 hours 5, 3

The single 1.5 mg dose is now the preferred approach because it eliminates the risk of missing the second dose and has equivalent efficacy to the split-dose regimen 4, 6.

Mechanism of Action

Levonorgestrel works primarily by preventing or delaying ovulation when taken before the preovulatory LH surge 5, 7. It may also affect sperm migration and fertilization 7. Critically, it does not disrupt an established pregnancy and will not work if you are already pregnant 2.

Efficacy

• Prevents approximately 85% of expected pregnancies when taken as directed 5, 2
• About 7 out of 8 women who would have become pregnant will not become pregnant 2
• Efficacy is time-dependent: effectiveness decreases progressively from 0-24 hours, 25-48 hours, and 49-72 hours post-intercourse 3

Important Efficacy Limitations

Women with obesity face reduced effectiveness: Data show levonorgestrel EC loses effectiveness in women weighing >165 lbs and may be ineffective in women >176 lbs 5. In these patients, ulipristal acetate (30 mg) is more effective and should be preferentially recommended 8. Note that doubling the levonorgestrel dose to 3 mg does not improve outcomes in obese individuals 9.

Contraindications

The only absolute contraindication is:

• Known allergy to levonorgestrel or any tablet ingredient 2

Levonorgestrel is NOT contraindicated in pregnancy—if inadvertently taken during early pregnancy, it causes no harm to the woman or fetus 5. A pregnancy test is not required before administration 5.

Drug Interactions Requiring Caution

Patients taking the following medications may have reduced levonorgestrel effectiveness 2:

• Efavirenz (HIV medication)
• Rifampin (tuberculosis treatment)
• Anticonvulsants (epilepsy medications)

For these patients, consider prescribing ulipristal acetate or a copper IUD instead, as these are not affected by enzyme-inducing drugs 2.

Common Side Effects

Expected side effects include 2:

• Menstrual changes: Period may be heavier, lighter, earlier, or later than expected
• Nausea (less common than with combined estrogen-progestin regimens)
• Lower abdominal pain
• Fatigue
• Headache
• Dizziness
• Breast tenderness

Follow-Up and Warning Signs

Expected next menstruation: Should occur at the expected time or within 1 week 2

Red flags requiring immediate evaluation:

• Period delayed >1 week: Obtain pregnancy test 2
• Severe abdominal pain: May indicate ectopic pregnancy—requires immediate medical attention 2

Clinical Pearls

• This is NOT regular contraception: Levonorgestrel EC should only be used as backup/emergency contraception, not as an ongoing contraceptive method 1, 2
• Advance provision is recommended: Provide advance prescriptions during routine care to minimize treatment delays 8, 5, 3
• No protection against STIs: Does not protect against HIV or other sexually transmitted infections 2
• Can be used multiple times: No medical contraindication to repeated use in the same cycle, though regular contraception is more effective 3
• Over-the-counter availability: Available without prescription for all women of childbearing potential in the United States 5

When to Choose Alternative Emergency Contraception

Consider ulipristal acetate (30 mg) instead when 8:

• Patient presents 72-120 hours after unprotected intercourse
• Patient has BMI ≥30 or weight ≥165 lbs
• Patient is taking enzyme-inducing medications

Consider copper IUD when 3:

• Patient desires ongoing highly effective contraception
• Patient presents within 5 days of unprotected intercourse (most effective EC option)