Levonorgestrel is the generic form of the emergency contraceptive commonly known as the morning-after pill. It is a backup birth control method taken after sexual intercourse to delay or inhibit ovulation and prevent pregnancy.
Levonorgestrel is a progestin medication that works in several ways to prevent post-coital pregnancies. One of the mechanisms is inhibiting the hormones that stimulate the normal ovulation process, causing a delay in the development of the egg and its release from the ovary into the fallopian tubes. It also thickens the cervical mucus, which interferes with the passage of sperm into the uterus and prevents fertilization. Levonorgestrel is not effective in terminating an existing pregnancy.¹
This guide pertains specifically to the use of levonorgestrel (Plan B) emergency contraception. It does not cover other common forms of the drug, such as oral contraceptive pills, transdermal patches, drugs for vaginal insertion, and intrauterine devices.
Levonorgestrel has been approved by the US Food and Drug Administration (FDA) for use as emergency contraception to prevent pregnancy after unprotected sex or contraceptive failure. When taken within 72 hours after unprotected sex, the drug has an 89% effectiveness rate.² ³
Plan B One-Step (levonorgestrel) is available over the counter (OTC) for patients of any age to purchase without a prescription.⁴
Levonorgestrel is available in two strengths, both in tablet form for oral use:
Two dose tablets: Two 0.75mg tablets taken 12 hours apart (generic)⁵
One dose tablets: One 1.5mg tablet taken in one dose (generic, Plan B One-Step, My Way)⁶
The drug should be taken as soon as possible, and within 72 hours of sexual intercourse, for maximum effectiveness.⁷
Take levonorgestrel as soon as possible after unprotected sexual intercourse. Aim to take it within 72 hours. This medication is designed to be taken as an emergency form of post-intercourse contraception and is not intended for use as routine birth control.⁸
The use of levonorgestrel is contraindicated for women who are pregnant, have undiagnosed abdominal pain or vaginal bleeding, and those with known hypersensitivity to the drug.⁹
Women with the following conditions may require caution when taking levonorgestrel:¹⁰
The most common side effects of levonorgestrel include the following:¹¹
Heavier menstrual flow
Nausea or vomiting
Headache or migraine
Vaginal discharge or spotting
Missed or delayed menstrual period
Heavier than usual menstrual bleeding
Less common adverse reactions include:¹²
Painful menstrual bleeding
Swelling and hives
An overdose of levonorgestrel is unusual but may occur in certain circumstances. For example, when a consumer does not follow the manufacturer's labeling and takes more than directed. Overdoses with oral contraceptive drugs have adverse effects similar to those already mentioned, especially nausea and vomiting, but the consequences are relatively minor due to the low toxicity of the drug.¹³ ¹⁴
You should not take this medication if you have ever experienced an allergic reaction to levonorgestrel or any of its ingredients.¹⁵
Symptoms of a drug allergy may include any of the following:
Skin rash, peeling, itching, or hives
Swelling of the lip, tongue, or throat
Difficulty breathing or wheezing
Rapid heart rate
Loss of consciousness
If you develop any symptoms of an allergic reaction after taking levonorgestrel, call your doctor or 911, or go to the closest emergency department, depending on the severity.
Levonorgestrel is not intended for long-term use. To prevent unwanted pregnancies on an ongoing basis, speak with your doctor about beginning a prescription birth control regimen.
Levonorgestrel is not an abortion pill and is not effective for terminating an established pregnancy. It is only effective in preventing pregnancy if taken as directed.¹⁶
Levonorgestrel is contraindicated for use during pregnancy or suspected pregnancy. No adverse effects have been seen in the pregnancies of patients who have taken the drug for contraception while unaware of their pregnancy. However, the label does warn those with abdominal pain to seek evaluation for ectopic pregnancy if a pregnancy ensues after taking levonorgestrel. Ectopic pregnancy symptoms to watch for include pelvic pain and vaginal bleeding.¹⁷ ¹⁸
Though levonorgestrel is present in breast milk, the dose levels are below the highest acceptable range. Although human studies are limited, no adverse effects on breastfeeding infants have been seen. The current recommendation is to avoid breastfeeding for three to four hours after taking the drug.¹⁹ ²⁰
Some medications may interact negatively with levonorgestrel. Note the following drugs and herbal supplements that may interfere with its effectiveness:²¹ ²² ²³
Sedatives such as Fiorinal, Pentothal, and Seconal
Diabetes medications, including pioglitazone (Actos) and exenatide (Bydureon)
Antibiotics like minocycline (Minocin), dicloxacillin (Dynapen), nafcillin (Nafcil), and rifampin (Rifadin)
Antiviral medicines to treat HIV infection, such as etravirine (Intelence), efavirenz (Sustiva, Stocrin), lopinavir/ritonavir (Kaletra), and others
Antifungals like griseofulvin (Fulvicin)
St. John's wort, Asian ginseng, garlic, gingko, echinacea, and danshen
Drugs used to treat cancer, such as apalutamide (Erlead), belzutifan (Welireg), and bexarotene (Targretin)
Medications for pulmonary arterial hypertension, such as bosentan (Tracleer, Safebo)
Steroids like prednisone
There is no formal recommendation not to drink alcohol when taking levonorgestrel.
Levonorgestrel is available without a prescription, so you won’t need to see your doctor before you take it. However, if this is your first time taking levonorgestrel, discussing your medical history and any current medications or supplements with your doctor may help determine if it is safe and appropriate for you.
Here are some specific topics to discuss before starting levonorgestrel:
Known allergies and previous adverse reactions to medications
All medications, herbs, supplements, and vitamins you take, including those you use occasionally
Your recent sexual activity and contraceptive use and your menstrual history
1982: Levonorgestrel earned US FDA approval²⁴
1999: The brand Plan B was approved for use as an emergency contraceptive (available by prescription only)²⁵
2006: Plan B became available OTC for women 18 years and older²⁶
2009: Plan B One-Step (a packaged medication containing one tablet) replaced Plan B (two tablets), and the drug was made available without a prescription for adolescents and women aged 17 years and older and with a prescription for younger patients²⁷
2013: The US FDA approved Plan B One-Step to be available OTC without a prescription for all ages²⁸
Take levonorgestrel as soon as possible after sexual intercourse, as it is less effective if taken more than 72 hours after unprotected sex.
Taking levonorgestrel with food may be helpful to avoid nausea. If vomiting occurs within two hours of ingestion, contact your physician to determine if you should take a second pill.
Certain medications make levonorgestrel less effective. Consult your doctor if you’re taking other medications.
Levonorgestrel may cause the next menstrual cycle to start a little earlier or later, and the amount of bleeding may be different than usual.
If your next period is more than one week late, you should take a pregnancy test or schedule an evaluation with your doctor.
Levonorgestrel does not prevent sexually transmitted infections. A condom must be used to provide some protection.
Yes, you can get pregnant after taking an emergency contraceptive. You should avoid sexual intercourse until you start another contraceptive regimen to prevent pregnancy.
There are no signs or symptoms to let you know if levonorgestrel worked. You’ll need to wait until your next period or take a pregnancy test.
Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.
However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.
It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.
Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.