Plan B (Levonorgestrel) — Emergency Contraception for the UK

Plan B is a commonly used form of emergency contraception containing levonorgestrel. It is designed to reduce the chance of pregnancy after unprotected sex or contraceptive failure. This guide explains how Plan B works, when to take it, what to expect, and important safety information.

If you’re unsure about what’s right for you, consider speaking to a pharmacist or clinician. This product information is provided to help you make an informed choice.

At a glance

• What it is: Emergency contraception (levonorgestrel)
• When to take it: As soon as possible after unprotected sex
• Most effective: Earlier is better
• Common dose: Typically a single dose
• Time to act: Works mainly by delaying ovulation
• Does not protect: Against future sex acts

Basic product information

How Plan B works (mechanism of action)

Plan B contains levonorgestrel, a synthetic progestogen (a hormone similar to progesterone). Its main mechanism is to delay ovulation—the release of an egg from the ovary.

Key points about how it works:

• Delays ovulation: If ovulation has not yet occurred, levonorgestrel may delay egg release.
• May affect sperm/egg: It can also influence the timing of ovulation and the environment in the reproductive tract.
• Timing matters: The earlier you take it after sex, the more likely it can prevent pregnancy.
• Not effective after ovulation: If ovulation has already happened, Plan B is less likely to work.

Pharmacokinetics (how the body processes it)

After taking levonorgestrel by mouth, it is absorbed through the digestive tract and reaches peak blood levels within a few hours. The hormone is then distributed in the body, where it is metabolised—primarily in the liver—and eliminated mainly via urine and bile.

Clinically, you don’t need to calculate levels or monitor anything at home. The most important factors are:

• Speed of taking the dose (earlier provides more benefit)
• Whether you may already have ovulated
• Whether you vomit soon after taking it

Typical use in the UK

Plan B is used as emergency contraception after events such as:

• Unprotected vaginal sex
• Condom breakage or slipping
• Missed or late contraceptive pills (depending on the type and how late)
• Misuse of contraception (for example, taking pills incorrectly)
• Other contraceptive failure

Plan B should be used as soon as possible after the incident. It is intended for occasional use, not ongoing contraception.

Timing: when should you take it?

Plan B is generally recommended as emergency contraception within 72 hours (3 days) after unprotected sex. Effectiveness decreases as time passes.

Practical timing guidance

• Best option: Take the dose immediately after you can.
• Within 24 hours: Typically offers the highest effectiveness.
• After 24–72 hours: Still may help, but the chance of pregnancy is higher than when taken earlier.

If you’re outside 72 hours

Some emergency contraception options may be effective up to 5 days (120 hours), depending on the method. If it has been more than 3 days since unprotected sex, consider speaking to a pharmacist or service provider promptly to discuss the best option for your situation.

Food interactions

Food does not generally prevent levonorgestrel from working. Plan B can usually be taken with or without food. However, if you vomit soon after taking it, the dose may not have been fully absorbed.

If you vomit shortly after taking Plan B:

• Seek advice from a pharmacist or the patient information leaflet for the exact timing of when to repeat dosing.
• Do not wait for symptoms—prompt advice is important to maintain effectiveness.

Alcohol and medicine interactions

For most people, moderate alcohol intake is not known to directly reduce levonorgestrel effectiveness. However, alcohol can lead to vomiting or missed doses, which may indirectly affect how well the medicine works.

When alcohol may be an issue

• Vomiting: If alcohol causes vomiting soon after taking Plan B, absorption may be reduced.
• Adherence: If you become unwell or forget the dose, effectiveness may be impacted.

Medicine interactions (important)

Some medicines can reduce the effectiveness of levonorgestrel by changing liver metabolism. Particularly relevant are medicines that are enzyme inducers.

Tell your pharmacist if you take any of the following (this is not an exhaustive list):

• Some medicines for epilepsy (anti-seizure medications)
• Rifampicin and other certain antibiotics
• St John’s wort (herbal product)
• Some HIV medicines
• Other medicines that may affect liver enzymes

If you are taking liver enzyme-inducing medicines, you may be advised to consider an alternative emergency contraception option, depending on availability and timing.

Indications: who can use it?

Plan B is indicated for emergency contraception in women and people who can become pregnant after: unprotected sex or contraceptive failure.

It is most suitable when taken within the recommended time frame after the event. It may be less effective if ovulation has already occurred.

Not all situations are the same. For example, if you are already on certain ongoing hormonal contraception methods, or if you have taken enzyme inducers, you may need tailored advice. A pharmacist can help you choose the best option.

Dosing: how to take Plan B

Typical dosing for Plan B (levonorgestrel) is:

• Adults and people of reproductive potential: Usually one tablet containing 1.5 mg levonorgestrel, taken as a single dose.
• Take it as soon as possible after unprotected sex.

What if you have a second incident?

Plan B does not protect against pregnancy from sex that happens after you take it. If you have more unprotected sex in the days following your dose, you may need additional emergency contraception advice. Consider using condoms until you can start or resume reliable contraception.

After taking Plan B: what to expect next

• Period timing: Your next period may come earlier or later than expected.
• Bleeding changes: You may have spotting or changes in flow.
• Possible side effects: Nausea, headache, dizziness, breast tenderness, lower abdominal pain, or fatigue.

Safety profile and side effects

Plan B is generally well tolerated. Like all medicines, it can cause side effects, although not everyone experiences them. Most side effects are temporary.

Common side effects

• Nausea
• Headache
• Fatigue
• Dizziness
• Lower abdominal pain
• Breast tenderness
• Spotting or changes in bleeding

Seek urgent medical advice if you experience

Most people do not develop serious complications. However, you should seek prompt medical help if you develop symptoms that could suggest a serious condition, including:

• Severe or persistent abdominal pain (especially one-sided)
• Fainting, dizziness, or unusual shoulder pain
• Very heavy bleeding
• Signs of an allergic reaction such as swelling of the face/lips, trouble breathing, or rash

Pregnancy after emergency contraception

If you become pregnant, you should discuss options with a healthcare professional. Emergency contraception is not intended to end an existing pregnancy.

If your period is delayed by more than a few days or you have symptoms of pregnancy, take a pregnancy test to be sure.

Practical use tips (make it work for you)

• Act quickly: Take Plan B as soon as possible after unprotected sex.
• Check timing: It is generally for use within 72 hours.
• Don’t double up unnecessarily: Follow the instructions provided with your product. If you vomit soon after taking it, get advice promptly.
• Plan for contraception going forward: Emergency contraception does not provide ongoing protection. Use condoms or start reliable contraception when appropriate.
• Know what to expect: Period changes can happen—don’t panic, but do take a test if your period is late.
• Consider interactions: If you take enzyme-inducing medicines or herbal supplements (like St John’s wort), talk to a pharmacist quickly—an alternative may be recommended.

Alternative emergency contraception options

Depending on how long it has been since unprotected sex, your medical history, and medication interactions, other emergency contraception options may be more suitable. Discuss options promptly if timing is near or beyond the 72-hour window.

Common alternatives

• Ulipristal acetate (another emergency contraception medicine):
  • May be suitable for use later into the time window than levonorgestrel.
  • May have different effectiveness where ovulation is closer.
• Levonorgestrel vs. copper IUD (intrauterine device):
  • A copper IUD can be used as emergency contraception up to 5 days after unprotected sex and provides ongoing contraception if kept in place.
  • Availability and suitability depend on assessment by a clinician.

The best choice is influenced by time since sex, body weight and BMI considerations (where relevant), medicine interactions, and personal circumstances. A pharmacy or sexual health clinic can help you choose.

Market and legal context in the United Kingdom

Emergency contraception is widely available in the UK. You can often access emergency contraception through:

• Pharmacies (including via staff advice and local service arrangements)
• GP services
• Sexual health clinics
• Out-of-hours services when appropriate

Regulations, packaging, and availability can vary by brand and formulation, and the method of supplying it may depend on local policies. Online pharmacy delivery may also be subject to eligibility checks and product-specific requirements.

Recent guidance (UK context)

UK guidance generally emphasises the same core principles:

• Earlier is better: take emergency contraception as soon as possible.
• Offer the right option for the time window: some methods may remain effective later than others.
• Consider interactions: enzyme-inducing medicines can reduce effectiveness of some hormonal emergency contraception.
• Follow-up: pregnancy testing if a period is late, and advice about contraception after the incident.

Because guidance can evolve, it’s a good idea to check the leaflet supplied with your specific product and ask a pharmacist if you have questions about your situation.

Delivery and availability

Availability of emergency contraception can vary by product and supplier. When ordering online:

• Choose the correct product: Ensure it contains levonorgestrel.
• Delivery speed matters: Because time is critical, select the fastest delivery option available.
• Check product packaging details: Confirm the dose strength and how it should be taken from the instructions provided.
• Keep the leaflet: It contains important information about vomiting, side effects, and follow-up.

If you need emergency contraception urgently, consider contacting a pharmacy or local sexual health service as well, especially if delivery may take longer than the recommended time frame.

FAQ: Plan B (Levonorgestrel)

1) How quickly does Plan B work?

Plan B works mainly by delaying ovulation. It begins working soon after taking the tablet, but the effectiveness depends strongly on how soon you take it after unprotected sex. Taking it immediately provides the best chance of preventing pregnancy.

2) Can I take Plan B if I’m breastfeeding?

Levonorgestrel is sometimes used during breastfeeding, and many healthcare providers consider it a reasonable option. For personal advice—especially if you’re taking other medicines—speak to a pharmacist or clinician.

3) What if my period is late?

If your period is more than a few days late, or if you have symptoms of pregnancy, take a pregnancy test. If it’s positive or you’re unsure, seek medical advice.

4) Will Plan B affect my fertility?

Plan B does not have a permanent effect on fertility. It is intended to reduce pregnancy risk from a specific recent incident by delaying ovulation at that time.

5) Does Plan B cause an abortion?

Plan B is emergency contraception meant to prevent pregnancy by delaying ovulation. It is not intended to end an existing pregnancy.

6) Can I take Plan B more than once?

Emergency contraception can be taken when needed, but it is not a substitute for ongoing contraception. Repeated use may cause more irregular bleeding and is less reliable than regular contraceptive methods.

7) What if I vomit after taking it?

Vomiting soon after taking Plan B may reduce absorption. Check the product leaflet for the recommended action based on how soon you vomited. In general, you should get prompt advice from a pharmacist.

8) Can I take Plan B with other medicines?

Some medicines can reduce effectiveness, particularly enzyme inducers (for example certain anti-epileptics, rifampicin, and St John’s wort). If you take any regular medicines or supplements, ask a pharmacist to confirm suitability.

9) Does alcohol stop it working?

Alcohol does not typically directly prevent levonorgestrel from working. However, if alcohol causes vomiting soon after taking Plan B, that may reduce absorption and effectiveness.

10) What contraception should I use afterwards?

After emergency contraception, you should use reliable contraception for ongoing protection. Condoms are a good immediate option. A pharmacist or clinic can advise when and how to start or resume ongoing contraception.

11) Is Plan B effective for everyone?

Effectiveness varies. It is generally less effective if taken later in the recommended window and may be reduced if ovulation has already occurred or if you take certain interacting medicines. If you have concerns, seek prompt advice.

When to seek further help

Contact a pharmacist, GP, or sexual health service if you:

• Are unsure about timing and the best option
• Take medicines that may interact with levonorgestrel
• Have severe symptoms after taking emergency contraception
• Have a delayed period or think you may be pregnant

Important: This page provides general information. Always read the patient information leaflet supplied with your specific product for the most accurate instructions for that formulation. If you have any concerns about side effects, interactions, or pregnancy risk, seek advice from a qualified healthcare professional.