Plan B (Generic Levonorgestrel): Complete Medication Guide
Key Takeaways
Plan B is an emergency contraceptive that may prevent pregnancy when taken within 72 hours of unprotected intercourse
It contains levonorgestrel, a synthetic hormone that works by delaying or preventing ovulation
Most effective when taken as soon as possible after unprotected sex
Available over-the-counter without age restrictions or prescription
Common side effects include nausea, headache, and irregular bleeding
Plan B Overview
Plan B (generic levonorgestrel) is an emergency contraceptive medication designed to help prevent pregnancy after unprotected intercourse or contraceptive failure. It belongs to a class of medications called progestins—synthetic hormones that mimic progesterone, a natural hormone in your body. This medication is not intended for routine birth control and should only be used in emergency situations.
Levonorgestrel works primarily by preventing or delaying ovulation, the release of an egg from your ovary. By stopping ovulation from happening, the medication prevents sperm from fertilizing an egg. It may also thicken cervical mucus, making it harder for sperm to reach an egg. Plan B is most effective when taken within 72 hours of unprotected intercourse, though some studies suggest it may work up to 120 hours. The sooner you take it after unprotected sex, the better your chances of preventing pregnancy.
This medication is available over-the-counter at pharmacies, supermarkets, and online retailers without a prescription. Unlike generic vs brand-name drugs, both generic and brand-name versions contain the same active ingredient and work equally well. Plan B is not an abortion pill—it prevents pregnancy from occurring rather than ending an existing pregnancy.
Side Effects
Most people tolerate Plan B well, with side effects typically being mild and temporary. Here's what you should know about potential reactions.
Common Side Effects
Nausea or upset stomach — Feeling sick to your stomach is one of the most frequently reported side effects; taking the medication with food may help reduce this
Headache — Mild to moderate headaches may occur within hours of taking the medication
Fatigue or dizziness — Some people experience tiredness or lightheadedness after taking Plan B
Breast tenderness — Your breasts may feel sore or sensitive for a few days
Irregular bleeding or spotting — You may experience unexpected bleeding or changes to your menstrual cycle timing
Serious Side Effects
Severe abdominal pain — Intense cramping or pain in your lower abdomen could indicate a serious condition and needs immediate evaluation
Chest pain or shortness of breath — These symptoms may indicate a blood clot or other serious condition requiring emergency care
Severe allergic reaction — Swelling of face, lips, or throat, difficulty breathing, or severe rash requires immediate medical attention
Vision changes — Sudden vision loss or other eye problems may occur, though rarely
When to Seek Medical Attention
Contact your healthcare provider if you experience severe abdominal pain, as this could indicate an ectopic pregnancy or other serious condition. Seek emergency care immediately if you develop chest pain, shortness of breath, or severe allergic symptoms.
If you don't get your period within three weeks of taking Plan B, take a pregnancy test and contact your doctor. This medication may not work if you're already pregnant, and it's important to confirm whether pregnancy prevention was successful.
Dosage
Dose Level or Form |
Dose |
Key Detail |
Standard dose (tablets) |
1.5 mg levonorgestrel as a single tablet |
Take as soon as possible, preferably within 72 hours of unprotected sex |
Alternative dosing |
0.75 mg tablets (take 2 tablets) |
Some formulations require two tablets; check package instructions |
Timing window |
Most effective within 72 hours |
May work up to 120 hours, but effectiveness decreases with time |
With or without food |
May be taken with or without food |
Taking with food may reduce nausea |
Important: Take Plan B as a single dose at one time—do not split the dose throughout the day. If you vomit within two hours of taking the medication, contact a healthcare provider about whether you need another dose. Plan B is emergency contraception only and should not be used as regular birth control. Do not delay taking this medication; effectiveness decreases significantly after 72 hours.
Drug Interactions
Plan B may interact with certain medications, potentially reducing its effectiveness. It's important to inform your healthcare provider about all medications you're taking.
Enzyme-Inducing Medications
Some medications like rifampin, phenytoin, and carbamazepine may decrease Plan B's effectiveness by speeding up how your body processes levonorgestrel. If you're taking these medications, Plan B may not work as well, and your doctor may recommend alternative emergency contraception options.
Certain HIV and Hepatitis C Medications
Antiretroviral drugs and protease inhibitors used to treat HIV or hepatitis C may interfere with levonorgestrel absorption or metabolism. These interactions could reduce the medication's ability to prevent pregnancy, so discuss emergency contraception alternatives with your healthcare provider if you take these medications.
St. John's Wort (Herbal Supplement)
This herbal supplement used for mood support may reduce Plan B's effectiveness by increasing how quickly your body breaks down levonorgestrel. If you take St. John's Wort regularly, inform your doctor when seeking emergency contraception.
Other Hormonal Contraceptives
Taking Plan B alongside regular birth control pills or other hormonal contraceptives may affect your regular birth control's effectiveness. Avoid when you're taking levonorgestrel and discuss timing with your healthcare provider.
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Pros and Cons
Pros
Available without prescription — No need for a doctor's visit; purchase over-the-counter at pharmacies and online
Effective when taken early — Most effective within 72 hours and may work up to 120 hours of unprotected intercourse
Well-tolerated — Minimal side effects for most people, typically mild and temporary
Cost-effective alternative to brand-name drugs — Generic levonorgestrel is affordable and accessible
No age restrictions — Available to anyone regardless of age
Cons
Time-sensitive — Must be taken within 72-120 hours; effectiveness decreases rapidly with delay
Not 100% effective — Does not guarantee pregnancy prevention, especially if taken later in the window
No STI protection — Does not protect against sexually transmitted infections
Nausea and side effects — May cause uncomfortable side effects like nausea or headache
Not for regular use — Should only be used for emergency situations, not as primary contraception
Frequently Asked Questions
Get answers to common questions about Plan B and emergency contraception.
Take Plan B as soon as possible—ideally within 24 hours of unprotected intercourse. It's most effective within the first 72 hours but may work up to 120 hours (5 days). The longer you wait, the less effective it becomes. Every hour matters, so don't delay if you think you need it.
No, Plan B prevents pregnancy only and offers no protection against sexually transmitted infections like chlamydia, gonorrhea, or HIV. If you've had unprotected sex, consider getting tested for STIs and discuss prevention options like condoms with your healthcare provider for future protection.
Plan B will not work if you're already pregnant and will not harm an existing pregnancy. If you suspect you might be pregnant before taking Plan B, take a pregnancy test first. If you have a positive result, contact your healthcare provider.
If you vomit within two hours of taking Plan B, the medication may not have been fully absorbed. Contact your healthcare provider to discuss whether you need to take another dose or explore alternative options for emergency contraception.
Plan B may temporarily affect your regular birth control pill schedule and effectiveness. After taking Plan B, continue taking your regular birth control as scheduled. Some healthcare providers recommend using backup contraception (like condoms) for the remainder of your cycle to be safe.
The Bottom Line
Plan B (generic levonorgestrel) is an effective emergency contraceptive option for preventing pregnancy after unprotected intercourse, but timing is critical. Take it as soon as possible within 72 hours of unprotected sex for best results. While available over-the-counter and generally well-tolerated, remember that Plan B is for emergencies only and should not replace regular contraception or STI prevention. Generic vs brand name drugs offer the same protection—generic levonorgestrel works just as well as brand-name Plan B at a fraction of the cost. This information is educational and does not replace advice from your healthcare provider. If you have questions about emergency contraception, reproductive health, or other medical concerns, Doctronic's AI doctors are available 24/7 with free AI consultations and affordable video or text visits. Get started with expert guidance today.
