Plan B (Levonorgestrel) – Emergency Contraception (UK)

Plan B contains levonorgestrel, a medicine used to help prevent pregnancy after unprotected sex or contraceptive failure. It is designed for emergency use and works best the sooner it is taken.

This page provides patient-friendly information about how Plan B works, when to take it, safety considerations, and practical advice—tailored for people in the United Kingdom.

Basic product information

Active ingredient: Levonorgestrel

Common strength: 1.5 mg per tablet (single dose) (depending on the specific brand/pack size)

Type: Emergency contraceptive pill (ECP)

When to use: After unprotected sex, late/ missed contraception, or condom break/slip

Availability in the UK: Many levonorgestrel-only emergency contraceptive pills (including Plan B and similar brands) are available from pharmacies and online pharmacy services. Product availability may vary by retailer and local regulations.

What Plan B is used for (indications)

Plan B is indicated for emergency contraception to reduce the risk of pregnancy following events such as:

• Unprotected sex
• Condom failure (breakage, slip, or incorrect use)
• Missed contraceptive pills or missed doses
• Failure of a method (for example, a diaphragm/cap not used correctly)
• Sexual assault or any situation where you did not use effective contraception

Important: Plan B does not protect against future sex acts. You must use regular contraception going forward.

How Plan B works (mechanism of action)

Levonorgestrel is a progestogen (a type of hormone). In emergency contraception, levonorgestrel primarily works by:

• Delaying ovulation (the release of an egg)
• Reducing the chance of fertilisation by delaying the time when an egg would be available

If ovulation has already occurred, levonorgestrel may be less effective. This is one reason why timing is critical.

Pharmacokinetics (how the body handles it)

While individuals vary, levonorgestrel taken orally follows predictable steps:

• Absorption: Levonorgestrel is absorbed from the digestive tract after swallowing the tablet.
• Distribution: It circulates in the bloodstream bound to proteins.
• Metabolism: It is metabolised primarily in the liver.
• Elimination: Metabolites are eliminated mainly through the urine and faeces.

Key practical implication: Because the main action is on the timing of ovulation, the medicine’s effectiveness depends more on when you take it relative to your ovulation window than on day-to-day metabolism.

When to take Plan B (timing guidance)

Plan B is most effective when taken as soon as possible after unprotected sex.

• Best option: Take it within 24 hours
• Still useful: Take it up to 72 hours (3 days) after unprotected sex

Some guidance may extend the window depending on product and circumstances, but effectiveness generally decreases with time. In the UK, levonorgestrel emergency contraception is commonly advised up to 72 hours. If you are outside that window, consider other emergency contraception options (see “Alternative options” below).

If you vomit soon after taking Plan B: You may not have absorbed the full dose. If vomiting occurs within a short time after taking the tablet (often considered within 3 hours), contact a pharmacist for advice on whether another dose is needed.

Typical dosing (how to take it)

Plan B is typically taken as a single dose:

How to take: Swallow the tablet with water. You can usually take it with or without food.

Food interactions

Food generally does not significantly reduce the effectiveness of levonorgestrel emergency contraception. Taking it with food may help if you feel nauseous.

Nausea/vomiting: If vomiting occurs soon after taking the tablet, it may reduce absorption. Seek advice promptly to confirm whether you need another dose.

Alcohol and medicine interactions

Alcohol

There is no specific alcohol “interaction” that would be expected to directly neutralise levonorgestrel. However:

• Alcohol may worsen dizziness or , which can affect how you feel after taking Plan B.
• If you vomit after drinking, absorption may be reduced—seek advice if vomiting happens soon after taking the tablet.

Important medicine interactions (enzyme inducers)

Some medicines can reduce the effectiveness of emergency contraceptive hormones by increasing the breakdown of levonorgestrel in the liver. These are often called enzyme-inducing medicines.

Examples to discuss with a pharmacist:

• Some treatments for epilepsy (anti-seizure medicines)
• Certain medicines for tuberculosis
• Some medicines for HIV (certain regimens may interact)
• Rifampicin/rifabutin (commonly mentioned enzyme inducers)
• Often, St John’s wort (herbal remedy)

If you take a medicine known to interact: ask a pharmacist about the best emergency contraception option. In some situations, a non-hormonal emergency option may be recommended (see alternatives).

Other medicines: Always check the label or ask a pharmacist if you are unsure whether your medicines may interact.

Safety profile (what to expect, side effects, and when to seek help)

Most people tolerate Plan B well. Side effects are usually short-lived.

Common side effects

• Nausea
• Vomiting (not common, but may occur)
• Headache
• Dizziness
• Fatigue
• Breast tenderness
• Lower abdominal cramps
• Changes to your next period (earlier or later, lighter or heavier)

Spotting/bleeding: Some people experience light bleeding or spotting after taking levonorgestrel.

Serious or urgent symptoms

Get medical advice promptly (NHS 111 or urgent care) if you experience:

• Severe lower abdominal pain (especially if it is one-sided) and/or fainting
• Signs of an allergic reaction such as swelling of the face/lips, difficulty breathing, or widespread rash
• Persistent vomiting or inability to keep the tablet down

Important pregnancy note: If emergency contraception was taken and pregnancy still occurs, healthcare professionals may consider the possibility of ectopic pregnancy (pregnancy outside the womb) if symptoms such as severe pain occur. Seek advice if you have worrying symptoms.

Who should use caution

• Known allergy to levonorgestrel or any ingredients in the tablet
• If you are taking enzyme-inducing medicines (effectiveness may be reduced)
• Any history of serious hormone-related conditions should be discussed with a clinician/pharmacist for personalised guidance

Practical use tips (make it work better)

• Take it immediately: The earlier you take Plan B, the higher the chance of preventing pregnancy.
• Don’t delay for “maybe”: If you are unsure about timing, take it anyway—waiting reduces effectiveness.
• Plan for regular contraception: After taking Plan B, continue or start a reliable contraceptive method for future sex acts.
• Use condoms until contraception is established: If you’re starting a new method, condom use helps prevent pregnancy while your regular method takes effect.
• Consider weight/body composition factors if relevant: Effectiveness can be reduced for some people at higher body weight. If you are concerned, ask a pharmacist about options.
• Set a reminder for a pregnancy test: See the FAQ section for timing.

Follow-up: menstruation and pregnancy testing

After taking Plan B:

• Your next period may come earlier or later than expected.
• It may be lighter or heavier.

When to test:

• If your period is more than 7 days late than usual, take a pregnancy test.
• If you have symptoms of pregnancy (such as persistent nausea, breast tenderness, or unusual fatigue) or your period is very different from usual, consider testing even if timing is borderline.
• If you used emergency contraception but are worried, a pharmacist or clinician can guide you on next steps.

Alternative emergency contraception options

In the UK, there are different emergency contraception choices, and the best option may depend on timing, body weight, and medicine interactions.

1) Ulipristal acetate (UPA)

• Often effective up to 120 hours (5 days) after unprotected sex
• May be a better option if you are closer to (or beyond) 72 hours
• Interactions with certain hormonal contraception can occur, so check advice from a pharmacist

2) Copper IUD (intrauterine device)

• Can be used as emergency contraception
• Very effective, including after later timing
• Requires fitting by a trained healthcare professional

3) Repeat dosing

If you have repeated unprotected sex after taking Plan B, Plan B does not provide ongoing protection. Talk to a pharmacist about further emergency contraception options if needed.

If you are outside the typical levonorgestrel timing window or if your medicines may interact, asking for the most suitable alternative is recommended.

Market and legal context in the United Kingdom

In the UK, emergency contraception is widely accessible and publicly funded or offered through multiple routes depending on circumstances.

• Pharmacy access: Levonorgestrel emergency contraception is commonly available through community pharmacies.
• Online access: Many UK pharmacies offer online ordering and delivery services for emergency contraception products.
• Clinical guidance: National guidance supports timely access to emergency contraception and encourages taking it as soon as possible.

Regulatory status: Emergency contraceptive pills are regulated medicines. Availability, branding, packaging and exact formulation may vary by supplier.

Recent guidance and key messages (UK-focused)

UK-facing guidance consistently emphasises the following:

• Time matters: Take levonorgestrel emergency contraception as soon as possible after unprotected sex.
• Consider alternatives if needed: If you are beyond 72 hours or concerned about reduced effectiveness (for example, due to body weight or interacting medicines), ask about ulipristal acetate or a copper IUD.
• Ongoing contraception: Emergency contraception does not prevent pregnancy from future sex acts.
• Follow-up: Test for pregnancy if your period is delayed or if symptoms occur.

For personal medical advice, speak with a pharmacist or a healthcare professional.

Delivery and availability (UK)

Online pharmacies typically offer:

• Ordering: Place an order online with delivery details.
• Packaging: Many services use discrete packaging.
• Delivery times: Dispatch and delivery can vary depending on location and courier service.

Important: Because Plan B is time-sensitive, choose a provider that can deliver quickly if you are not able to obtain it immediately from a local pharmacy.

If you need it urgently and delivery is unlikely to arrive before the 72-hour window, consider getting it in person from a nearby pharmacy or asking about alternative options available faster.

FAQ – Plan B (Levonorgestrel) for the UK

1) How effective is Plan B?

Effectiveness depends on how soon you take it and where you are in your cycle. Taking it within 24 hours generally offers the best chance of preventing pregnancy. Effectiveness may be lower when taken later or if ovulation has already occurred.

2) Can I take Plan B more than once?

It is possible to use emergency contraception more than once if needed. However, it is not suitable as regular contraception. If you require emergency contraception repeatedly, consider a reliable ongoing method and discuss options with a pharmacist or GP/sexual health service.

3) What if I already started my period?

If you have already started bleeding and are within your normal cycle pattern, Plan B may still have some effect depending on whether ovulation is imminent. Because your cycle timing can vary, the best advice is to take it as soon as possible if you have had risk of pregnancy.

4) Will Plan B affect my next period?

Yes, it can. Your next period may arrive earlier or later than expected and may be heavier or lighter. If your period is more than 7 days late, take a pregnancy test.

5) If I vomit after taking it, what should I do?

Vomiting shortly after taking the tablet may mean you did not absorb the full dose. Contact a pharmacist for guidance on whether another tablet is needed.

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

Levonorgestrel emergency contraception is generally considered compatible with breastfeeding. If you have specific concerns (for example, about infant health or your medicines), speak with a pharmacist for reassurance and tailored advice.

7) Does Plan B work for everyone?

Plan B works best before ovulation. Effectiveness may be reduced in certain situations such as later timing, if ovulation has already happened, or if you take interacting medicines. If you are concerned about any of these factors, ask about alternatives like ulipristal acetate or a copper IUD.

8) Are there any long-term effects?

Plan B is designed for occasional emergency use. There is no expectation of long-term harm from a single dose when used correctly. Side effects, when they occur, are usually short-lived.

9) Can I keep using contraception after taking Plan B?

Yes. Plan B does not replace regular contraception. Continue your current method if you have one, or start a regular method as recommended by a pharmacist/clinician.

10) What if I had unprotected sex again after taking Plan B?

Plan B does not protect against future acts. If you have another risk event, consider additional emergency contraception and talk to a pharmacist for the most appropriate option based on timing.

Summary

Plan B (levonorgestrel) is an emergency contraceptive option available in the UK for use after unprotected sex or contraceptive failure. It mainly works by delaying ovulation and is most effective when taken as soon as possible (commonly up to 72 hours). Side effects are usually temporary, and a pregnancy test is recommended if your period is late.

If you have concerns about medicine interactions, timing, or reduced effectiveness, speak with a pharmacist promptly to find the most suitable emergency contraception option.