Emergency contraception is an essential option for preventing unwanted pregnancy after unprotected sex or contraceptive failure. The morning-after pill provides a safety net, but like all medications, it is not 100% effective. Many factors can reduce its effectiveness, including ovulation timing, body weight, and certain health conditions. Understanding these risks can help you make an informed decision about emergency contraception and improve its chances of success.

How Does the Morning-After Pill Work?

The morning-after pill works by delaying ovulation, preventing an egg from being released and fertilised. There are two main types available in the UK:

Levonorgestrel-based pills (such as Levonelle) – These contain a synthetic hormone similar to progesterone and should be taken within 72 hours of unprotected sex.

Ulipristal acetate pills (such as ellaOne) – These block the hormone progesterone, preventing ovulation, and can be taken up to 120 hours (five days) after unprotected sex.

Both types are more effective the sooner they are taken, but there are circumstances where they may not work as expected.

1. Timing in the Menstrual Cycle

The morning-after pill primarily works by delaying ovulation. If ovulation has already occurred, the pill will not be able to prevent pregnancy, as it does not stop fertilisation or implantation. This means that if you are close to ovulation or have already ovulated, emergency contraception may not be effective.

Ovulation typically occurs around the middle of the menstrual cycle, but it can vary. If you track your cycle and believe you are near ovulation, an alternative emergency contraceptive method, such as the copper intrauterine device (IUD), may be a better option as it works by preventing implantation.

2. BMI and Body Weight

Body weight and BMI (Body Mass Index) can influence the effectiveness of the morning-after pill. Research suggests that levonorgestrel-based emergency contraception may be less effective for individuals with a BMI over 26 or weighing more than 70kg. Ulipristal acetate (ellaOne) appears to be more effective than levonorgestrel in individuals with a higher BMI, but its effectiveness may also decrease with increasing weight.

For those who may be at risk of reduced effectiveness due to body weight, the copper IUD remains the most reliable form of emergency contraception, as it is not affected by BMI.

3. Vomiting After Taking the Pill

If you vomit within three hours of taking the morning-after pill, your body may not have absorbed it properly, reducing its effectiveness. In this case, you should take another dose as soon as possible. If vomiting persists, an alternative form of emergency contraception, such as the copper IUD, should be considered.

4. Drug Interactions

Certain medications can reduce the effectiveness of the morning-after pill. These include:

• Some epilepsy medications
• Certain HIV treatments
• Tuberculosis drugs
• St John’s Wort (a herbal supplement)

If you take any of these medications regularly, you may need a higher dose of levonorgestrel (two tablets instead of one) or consider alternative methods like the copper IUD. Speak to a pharmacist for personalised advice.

5. Unprotected Sex After Taking the Pill

Taking the morning-after pill protects you from one instance of unprotected sex. If you have unprotected sex again after taking the pill, it will not prevent pregnancy from the second encounter. You may need to take another dose or consider other contraception options to ensure protection.

6. Delayed Period or Signs of Pregnancy

While the morning-after pill is effective for many people, pregnancy is still possible. If your period is more than seven days late, lighter than usual, or unusually heavy, it is recommended to take a pregnancy test. If you experience symptoms such as nausea, breast tenderness, or fatigue, these may also indicate pregnancy, and you should seek medical advice.

How to Improve the Effectiveness of the Morning-After Pill

Take it as soon as possible – The earlier you take it after unprotected sex, the better it works.

Know where you are in your cycle – If you are close to ovulation, consider the copper IUD instead.

Check for medication interactions – Consult a pharmacist if you take any medications that could affect the pill’s effectiveness.

Have a backup plan – Use regular contraception to avoid needing emergency contraception frequently.

Why Speaking to a Pharmacist Helps

If you need emergency contraception, getting guidance from a trusted healthcare professional can help improve its success. At Home Ground Pharmacy, we offer confidential consultations to help you choose the most effective option based on your personal circumstances. Whether you need advice on timing, BMI considerations, or alternative methods like the copper IUD, we’re here to support you with expert guidance.

Visit us in-store or contact us online for discreet, professional advice on emergency contraception and your reproductive health.

Book your appointment now.

This blog was written on behalf of Home Ground Pharmacy by Pharmacy Mentor.