Levonorgestrel Explained: Complete Guide to Uses, Safety, and How It Works

Levonorgestrel Explained: Complete Guide to Uses, Safety, and How It Works

Levonorgestrel Effectiveness Calculator

How Effective Is Levonorgestrel?

Estimate the effectiveness of levonorgestrel emergency contraception based on how long after unprotected sex you take it. Effectiveness decreases the longer you wait.

Enter the number of hours since unprotected sex occurred
Important note: Effectiveness is highest when taken within 72 hours (3 days) of intercourse. This calculator provides estimates based on scientific studies, but individual results may vary.

When it comes to preventing an unintended pregnancy after unprotected sex, few names appear as often as Levonorgestrel a synthetic progestin used in emergency contraception and certain hormonal IUDs. This guide walks you through what the hormone does, when to take it, how effective it is, and what to watch out for.

What is Levonorgestrel?

Levonorgestrel belongs to the class of hormones called Progestin synthetic compounds that mimic the activity of natural progesterone. First approved for medical use in the 1970s, it has become a staple in both emergency contraception pills (often sold as “Plan B” or “Ella”) and the hormonal intra‑uterine device (IUD) marketed under names like Mirena.

How Does Levonorgestrel Work?

In the body, levonorgestrel works by interfering with Ovulation the release of an egg from the ovary. If taken before the egg is released, the hormone can prevent it from reaching the fallopian tube, effectively stopping fertilization before it starts. When used after fertilization, it thickens cervical mucus and alters the uterine lining, making it less receptive to implantation.

Medical Uses of Levonorgestrel

There are three main ways levonorgestrel is prescribed:

  1. Emergency contraception a short‑term, high‑dose method to prevent pregnancy after unprotected sex. A single dose (1.5 mg) or two‑dose regimen (0.75 mg 12 hours apart) is typical.
  2. Hormonal IUD an intra‑uterine device that releases levonorgestrel over several years. These devices provide both ongoing birth control and a lighter, more predictable menstrual flow.
  3. Off‑label support for treating irregular menstrual cycles or endometriosis, though this is less common.

Dosage Forms and How to Take Them

Emergency contraception pills come in two common brands:

  • Plan B One‑Step - 1.5 mg levonorgestrel in a single tablet.
  • Ella - 1.5 mg levonorgestrel in a single tablet, approved for use up to 120 hours (5 days) after intercourse.

The IUD version, such as Mirena a levonorgestrel‑releasing intra‑uterine system, is inserted by a clinician and can remain effective for up to 5 years.

Illustration of levonorgestrel blocking an egg and thickening cervical mucus in a cartoon uterus.

Effectiveness and Timing

When taken within 72 hours, levonorgestrel emergency pills reduce the chance of pregnancy by roughly 75‑89 %. The effectiveness drops after 72 hours but remains higher than doing nothing. The IUD, on the other hand, is over 99 % effective at preventing pregnancy from the moment of insertion.

If you’re wondering whether levonorgestrel is right for you, the key factor is how quickly you can access the pill. The sooner you take it, the better the odds.

Side Effects and Risks

Most people experience only mild, short‑term side effects such as:

  • Nausea or mild stomach upset.
  • Headache or dizziness.
  • Temporary spotting or changes in menstrual timing.

Serious reactions are rare but can include severe abdominal pain (which may signal an ectopic pregnancy), allergic rash, or pronounced mood swings. Women who are pregnant, have uncontrolled hypertension, or have a history of blood‑clotting disorders should avoid levonorgestrel unless a doctor advises otherwise.

Drug Interactions and Precautions

Levonorgestrel’s efficacy can be lowered by certain medications that affect liver enzymes, especially:

  • Rifampin (an antibiotic used for tuberculosis).
  • Certain anti‑epileptic drugs like carbamazepine and phenytoin.
  • St. John’s Wort, a popular herbal supplement.

If you’re on any of these, consider a copper IUD or a prescription‑only method like ulipristal acetate (another type of emergency pill).

Cartoon comparison of a levonorgestrel pill, hormonal IUD, and copper IUD with effectiveness captions.

Comparing Levonorgestrel with Other Options

Emergency Contraception Options Compared
Method Active Ingredient Window of Use Typical Failure Rate
Levonorgestrel pill Levonorgestrel Up to 120 hours (best < 72 h) 0.9‑2 %
Ulipristal acetate (Ella) Ulipristal Up to 120 hours 0.6‑1 %
Copper IUD Copper (non‑hormonal) Within 5 days 0.1 %

While levonorgestrel is widely available over the counter, the copper IUD offers the lowest failure rate. However, it requires a clinician for insertion and can cause heavier periods for some users.

Frequently Asked Questions

Can I use levonorgestrel if I am already pregnant?

No. Levonorgestrel will not terminate an existing pregnancy; it only works to prevent fertilization or implantation. If you discover you are pregnant, consult a healthcare provider about other options.

Will the pill cause my next period to be delayed?

It can. Some people get their period up to a week early or late. This is normal and does not mean the pill failed.

Is it safe to take levonorgestrel while breastfeeding?

Yes, the amount that passes into breast milk is minimal and not associated with adverse effects in infants. Nonetheless, discuss any concerns with your doctor.

How does levonorgestrel differ from the hormonal IUD?

The IUD releases a low, steady dose of levonorgestrel directly into the uterus, providing continuous birth control for years. The emergency pill delivers a high, single dose meant for one‑time use within a short window.

Can I take levonorgestrel if I have a history of blood clots?

Generally, a single emergency dose is considered low risk, but you should talk to a physician first because progestins can affect clotting factors in susceptible individuals.

Next Steps and Where to Get Levonorgestrel

In most countries, including Australia, levonorgestrel emergency pills are available without a prescription at pharmacies, clinics, and even some supermarkets. If you prefer a longer‑acting method, schedule an appointment with a GP or a family‑planning clinic to discuss IUD insertion.

Remember, the best protection is consistent, everyday use of a reliable contraceptive method. Levonorgestrel is a valuable safety net, but it’s not a substitute for regular birth control.