Approved indications: By mouth, levonorgestrel is approved as a single high‑dose tablet for emergency contraception after unprotected intercourse or contraceptive failure, and, when combined with ethinyl estradiol in daily oral contraceptive pills, to prevent pregnancy in people of reproductive age.

Off-label uses: Clinicians may recommend levonorgestrel emergency contraception up to 5 days after unprotected sex and may allow repeat use more than once in the same menstrual cycle; studies and guidelines support moderate effectiveness in these settings, while noting that protection declines the longer the delay and may be lower in people with higher body weight.

Efficacy expectations: For emergency contraception, when the 1.5 mg dose is taken within 72 hours, about 2–3 out of 100 users become pregnant, with highest effectiveness if taken within 24 hours and decreasing but still some protection up to 120 hours; combined levonorgestrel–ethinyl estradiol birth‑control pills used correctly result in fewer than 1 pregnancy per 100 users per year with perfect use and a few pregnancies per 100 per year with typical use, similar to other combined oral contraceptives.

Emergency contraception dosing: For adolescents and adults, the standard oral emergency‑contraception regimen is one 1.5 mg levonorgestrel tablet taken by mouth once, as soon as possible and within 72 hours after unprotected sex or contraceptive failure; it can be taken with or without food, although taking it with food may reduce nausea.

Ongoing contraception dosing: In combined levonorgestrel–ethinyl estradiol birth‑control pills, take one tablet by mouth every day at about the same time, following the specific pack schedule (for example, 21 or 24 active pills followed by placebo pills), and start the next pack on time without a gap unless your prescriber instructs otherwise.

Special instructions: If you vomit within about 2 hours after taking the 1.5 mg emergency tablet, contact a clinician or pharmacist to see if you should repeat the dose; after taking emergency levonorgestrel, use condoms or abstain from sex until you begin or resume a reliable regular contraceptive method, and take a pregnancy test if your period is more than about 1 week later than expected.

Missed doses: For emergency contraception there is no regular schedule—beyond possibly repeating the dose after vomiting—so you do not “make up” missed doses; for daily levonorgestrel‑containing combination pills, follow the patient insert, but in general take a missed active pill as soon as you remember, continue the pack, and use backup contraception if you have missed two or more active pills or started a pack late.

Overdose: Taking more levonorgestrel tablets than recommended is unlikely to be life‑threatening but can cause pronounced nausea, vomiting, and bleeding changes; in case of suspected overdose, contact Poison Control (1‑800‑222‑1222 in the U.S.) or seek medical attention.

Common side effects: With the single 1.5 mg emergency dose, common effects include nausea, abdominal or pelvic pain, fatigue, headache, dizziness, breast tenderness, and temporary changes in timing or heaviness of the next period; these are usually mild and resolve within a few days or by the next cycle.

Serious or rare adverse effects: Seek immediate care for severe one‑sided lower abdominal pain (possible ectopic pregnancy), very heavy or prolonged vaginal bleeding, signs of a serious allergic reaction (such as hives, facial or throat swelling, or trouble breathing), chest pain or shortness of breath, or sudden severe headache or vision changes (especially in users of estrogen‑containing combination pills).

Warnings and precautions: Do not use levonorgestrel emergency contraception if you are already known to be pregnant because it will not work, although accidental use in early pregnancy has not been shown to harm the fetus; talk with a clinician first if you have severe liver disease, unexplained vaginal bleeding, or a history of ectopic pregnancy. Levonorgestrel is considered compatible with breastfeeding and can be used by adolescents and adults, while estrogen‑containing levonorgestrel combination pills should usually be avoided in people who smoke and are over 35 or who have strong risk factors for blood clots, stroke, certain cancers, or uncontrolled high blood pressure.

Comparative safety: A single emergency‑contraception dose of levonorgestrel has a very low risk of life‑threatening events and is generally safer than continuing an unintended pregnancy; when taken long term in combined oral contraceptives, its overall safety profile is similar to other estrogen‑containing birth‑control pills and most serious risks are related to the estrogen component.

Reporting side effects: Side effects or suspected adverse reactions can be reported to the FDA MedWatch program (online or at 1‑800‑FDA‑1088), where updated safety information and drug safety communications are also posted.

Major drug interactions: Medicines that strongly increase liver enzyme activity can lower levonorgestrel levels and reduce effectiveness, including certain antiseizure drugs (such as carbamazepine, phenytoin, phenobarbital, primidone), tuberculosis treatments (rifampin, rifabutin), some HIV medications (such as efavirenz and certain protease inhibitors), and the herbal supplement St. John’s wort; people taking these should discuss alternative or additional contraceptive methods with a clinician.

Other medicines and substances: Some antibiotics or other drugs may modestly affect hormone levels in combined pills, and severe vomiting or diarrhea soon after an oral dose can reduce absorption; alcohol does not directly inactivate levonorgestrel but can increase the chance of missed or mistimed doses.

Precautions: Levonorgestrel emergency pills may be less effective in people with higher body weight or BMI or in those taking strong enzyme‑inducing medicines, so providers may recommend a copper IUD or ulipristal acetate instead when feasible; estrogen‑containing levonorgestrel combination pills are usually avoided in people with a history of blood clots, stroke, certain heart conditions, estrogen‑dependent cancers, severe liver disease, or uncontrolled high blood pressure.

Monitoring: No routine blood tests or imaging are needed after a single levonorgestrel emergency dose, but a pregnancy test is advised if no period occurs within about 3 weeks; with long‑term use of levonorgestrel‑containing oral contraceptives, clinicians typically check blood pressure before starting and periodically thereafter and may monitor other conditions (such as migraines, lipids, or liver function) based on individual risk.

Q: How soon do I need to take oral levonorgestrel after unprotected sex?
A: You should take the 1.5 mg emergency tablet as soon as possible—ideally within 24 hours and no later than 72 hours—for best protection, though there may still be some benefit up to 5 days after intercourse.

Q: Will levonorgestrel work if I am already pregnant, and does it cause abortion?
A: Levonorgestrel emergency contraception does not work if you are already pregnant and current evidence shows it does not harm an existing pregnancy, so it is not an abortion pill.

Q: Can I use levonorgestrel emergency contraception more than once in the same month?
A: Yes, it can be used more than once in a cycle if needed, but repeated use may lead to more irregular bleeding and is less effective and more expensive than using a reliable ongoing contraceptive method.

Q: Does taking levonorgestrel affect my future fertility?
A: Available data indicate that levonorgestrel, whether taken as a one‑time emergency dose or as part of birth‑control pills, does not cause long‑term infertility, and your ability to become pregnant returns to baseline once the hormone is out of your system.

Q: Does my weight change how well levonorgestrel emergency contraception works?
A: Levonorgestrel may be somewhat less effective in people who are overweight or obese, but it can still reduce pregnancy risk, and in higher‑weight users many clinicians prefer to offer a copper IUD or ulipristal acetate when those options are available.

Storage: Store levonorgestrel tablets at room temperature in their original blister packaging, away from moisture, heat, and direct light, and out of the reach of children and pets.

Handling: Keep the package where you can access it quickly in an emergency, and do not use tablets that are expired, discolored, chipped, or otherwise damaged.

Disposal: For unused or expired tablets, use a local medicine take‑back program when available; if none is available, place tablets (without crushing) in a sealed container mixed with something unappealing (such as used coffee grounds or cat litter) before putting in household trash, and do not flush them unless the package specifically instructs you to.