How Effective Is the Contraceptive Pill?

Reviewed by Usama Ali, MPharm (GPhC: 2224726). Last reviewed: October 2026.

The contraceptive pill is one of the most commonly used forms of contraception in the UK, but how effective is the pill at actually preventing pregnancy? Understanding what can affect your protection can help you use the pill as effectively as possible.

How effective is the pill?

According to the NHS, the contraceptive pill is over 99% effective with perfect use. This means fewer than 1 in 100 people using the pill correctly will become pregnant over the course of a year.

With typical use, the pill is around 91% effective, meaning around 9 in every 100 people using it will become pregnant in a year.

The difference between these figures comes down to how the pill is used.

Perfect use means following the instructions correctly all the time, including taking your pills as directed and starting new packs at the correct time.

Typical use reflects everyday life, where someone may occasionally forget their pill, take it late or make another mistake that affects their protection.

How effective is the combined pill?

The combined contraceptive pill contains oestrogen and progestogen and is over 99% effective when used correctly all the time.

It primarily prevents pregnancy by stopping ovulation, meaning an egg is not released from the ovaries. It also thickens cervical mucus and thins the lining of the womb.

With typical use, the combined pill is around 91% effective.

How effective is the mini pill?

Unsurprisingly, the mini pill is very similar in terms of effectiveness.

The mini pill, also known as the progestogen-only pill, is over 99% effective with perfect use and around 91% effective with typical use.

However, taking the mini pill at the correct time is particularly important. Depending on the type you use, there will be a specific window in which you need to take your pill to remain protected: 3 hours for a traditional mini pill, 12 hours for desogestrel and 24 hours for Slynd (FSRH).

Always follow the instructions provided with your particular pill and speak to a pharmacist if you're unsure.

What can make the pill less effective?

The contraceptive pill is highly effective, but several things can reduce your protection.

These can include:

• Missing pills or taking them incorrectly
• Starting a new pack later than instructed
• Vomiting shortly after taking your pill
• Having severe or prolonged diarrhoea
• Taking certain medicines or herbal remedies that interact with the pill

For example, some medicines used to treat epilepsy, tuberculosis (TB) or HIV can affect how well hormonal contraception works. The herbal remedy St John's wort can also interfere with the pill. Most antibiotics do not affect the pill, as our guide to the pill and antibiotics explains.

If you're prescribed a new medication or considering a herbal remedy, tell your pharmacist or healthcare professional that you take the contraceptive pill.

What if you miss a pill?

Missing a pill doesn't necessarily mean you'll become pregnant, but what you need to do next depends on the type of pill you're taking, how many pills you've missed and when you missed them.

You may need to take the missed pill as soon as possible and use additional contraception, such as condoms, for a period of time.

In some circumstances, emergency contraception may also be recommended.

Always check the patient information leaflet supplied with your pill or speak to a pharmacist if you're unsure what to do. Our guide on what to do if you miss a pill explains the rules for each type.

Can being sick affect how effective the pill is?

Yes. Vomiting or severe diarrhoea can prevent your body from absorbing the hormones in your pill properly.

Exactly what you need to do depends on whether you're taking the combined or mini pill, when you were sick and the specific pill you use. Our guide to vomiting, diarrhoea and the pill gives the timings for each type.

If you're unwell while taking the pill, check the instructions that come with your medication. A pharmacist can also advise whether you need to use additional contraception.

Is the pill 100% effective?

No contraceptive pill is 100% effective. When taken correctly, both the combined and mini pill are over 99% effective, but in everyday use around 9 in 100 people get pregnant each year. Long-acting methods such as the implant, IUD and IUS are also over 99% effective and do not rely on you remembering to take a pill.

The easiest way to maximise your protection is to follow the instructions for your particular pill carefully. Setting a daily reminder can also help you remember to take it consistently.

Remember that the contraceptive pill protects against pregnancy but does not protect against sexually transmitted infections (STIs). Condoms can help protect against STIs and can be used alongside the pill.

Find the right contraception for you

The contraceptive pill can provide highly effective protection against pregnancy when used correctly, whether you choose the combined or mini pill.

At Contraception Direct, you can book a free phone consultation with one of our contraception specialist pharmacists, who will help you find a pill that suits you. If the pill is suitable for you, it is posted free in discreet packaging, helping you access contraception safely and conveniently.

This information is for general guidance only and does not replace advice from a clinician, pharmacist, or doctor. A clinician will review your consultation before any medication is supplied.