Oral Contraceptive Pills (Birth Control Pills)
The Pill — What Every Woman Deserves to Know
Clear, honest answers about oral contraceptive pills — written for you, not for a textbook.
The Basics
What are oral contraceptive pills?
Oral contraceptive pills (often called “the pill”) are medicines taken daily to prevent pregnancy. They contain hormones named oestrogen and/or progestogen, similar to those naturally produced by your body.
There are two main types:
- Combined pill – contains estrogen and progestogen
- Progestogen-only pill (POP) – contains only progestogen
How do the pills prevent pregnancy?
The pill works in three main ways:
- Stops your ovaries from releasing an egg (ovulation)
- Thickens the mucus at the entrance of the womb, making it harder for sperm to enter
- Thins the lining of the womb, making it less likely for a pregnancy to develop
These actions together make pregnancy very unlikely when the pill is taken correctly.
How It Works
How effective is the pill?
When taken perfectly (at the same time every day without missing doses), the pill is over 99% effective at preventing pregnancy. With typical use (which includes occasional missed pills), it is about 91% effective, and about 9 in 100 women will get pregnant in a year. Taking the pill consistently and correctly improves its effectiveness.
The pill can also help with your acne, heavy or painful periods, PMS (premenstrual syndrome), and conditions like endometriosis.
What are the additional benefits of the pill?
The combined oral contraceptive pill is not only used to prevent pregnancy- it can also help manage certain common symptoms. Taking the pill regularly can make your menstrual periods more regular, lighter, and less painful.
It may also improve symptoms of the following conditions,
- Premenstrual syndrome (PMS); symptoms you experience in the days before your period starts, such as bloating (feeling full in your belly), breast tenderness, headaches, low energy, change in appetite, and mood swings
- Endometriosis
- Polycystic ovary syndrome (PCOS)
- Moderate to severe acne
If you experience heavy or painful periods or troublesome acne, you can speak with a doctor to find out whether the combined pill is a suitable option for you. They will assess your health and help you choose the safest and most appropriate treatment.
How do I take the pill?
Most combined pills are taken once daily for 21 days, followed by a 7-day break, during which you may have a withdrawal bleed similar to a period. Some packs contain 28 pills, including 7 inactive pills for convenience.
The progestogen-only pill is taken every day without a break, and it must be taken at the same time each day to work properly. Your doctor/midwife will explain which type is best for you and how to take it, depending on the brand.
Take your pill at the same time every day. Consistency is key to preventing pregnancy with the pill!
If you start taking the pill in the first 5 days of your cycle (day 1 is the first day of your period), you will be protected from pregnancy straight away. But if you start taking the pill more than 5 days after the beginning of your period, you will not be protected from pregnancy straight away.
You’ll need to use another type of contraception, such as condoms, until you’ve taken the pill for 7 days.
If there’s a chance you could already be pregnant when you start taking the pill, take a pregnancy test 3 weeks after the last time you had unprotected sex.
When you stop taking the pill, your fertility usually returns to previous levels after about a month.
What should I do if I miss a pill?
If you miss a pill or take it late, what you need to do depends on:
- The type of pill you are using
- How many pills you have missed
- Where you are in the pack (which week)
For clear guidance, check the leaflet that comes with your pill or if you miss more than one pill, speak to your doctor.
You may need to:
- Take the missed pill as soon as you remember
- Use additional contraception (such as condoms)
- Consider emergency contraception in some situations
What if you take an extra pill?
Taking more than one pill by mistake is unlikely to cause harm.
However, you may:
- Feel nauseous or vomit
- Have some unexpected vaginal bleeding
If you feel unwell or have concerns, seek advice from a doctor.
What should you do if you are sick or have diarrhoea while taking the pill?
Being unwell can affect how well the combined pill works.
If you vomit (are sick):
If you are sick within 3 hours of taking your pill, take another pill as soon as possible. Then continue the rest of your pills at the usual time. If vomiting continues, use additional contraception (such as condoms) until you have taken the pill correctly for 7 days without being sick.
If you have diarrhoea:
If diarrhoea lasts more than 24 hours, continue taking your pill as normal. Use additional contraception (such as condoms) until 7 days after the diarrhoea has stopped.
If illness happens near your pill-free break:
- If you are sick or have diarrhoea for more than 24 hours while taking the last 7 active pills in your pack: Finish those pills as usual. Start your next pack immediately. Do not take a pill-free break or inactive pills
- Use additional contraception until you have taken the pill correctly for 7 days without symptoms.
If you are unsure what to do, seek advice from your doctor.
Are there any serious risks?
The combined oral contraceptive pill is safe for most people. However, like all medications, it has some risks. These are uncommon, and your doctor or pharmacist will check if the pill is suitable for you before starting it.
Blood clots– The risk of a blood clot is very small (up to about 1 in 1,000 users). Clots can occur in the leg or lung, in the heart (causing a heart attack), or in the brain (causing a stroke). You should seek medical help urgently if you develop symptoms such as severe leg pain, chest pain, or sudden breathlessness.
The pill may slightly increase the risk of breast cancer and cervical cancer, but this risk returns to normal about 10 years after stopping the pill.
The pill can also reduce the risk of certain cancers, including: womb (uterus) cancer, ovarian cancer, and bowel cancer
Who should not take the combined pill?
You may be advised not to take it if you:
- Smoke and are over 35
- Have a history of blood clots
- Have certain types of migraine
- Have high blood pressure or certain medical conditions
The doctor will always check if the pill is safe for you before starting it.
Does the pill protect against sexually transmitted infections (STIs)?
No. Hormonal contraceptive pills do not stop you from getting or passing on sexually transmitted infections (STIs). Using condoms is recommended to reduce the risk of infections.
Can I take the pill after having a baby?
Yes, but timing depends on whether you are breastfeeding and your risk of blood clots. Your doctor will advise the safest option and timing for you.
Can other medicines affect the pill?
Yes. Some medicines can reduce how well the pill works and the pill may not work properly to stop you from getting pregnant. Inform your doctor if you are prescribed or currently taking,
- Medicine for TB (Tuberculosis)
- Medicine for Epilepsy
- Medicine for HIV
- Certain antifungals (Griseofulvin)
- Lamotrigine (Mood stabilizer)
- Herbal remedies like St John’s Wort
When should I seek medical advice?
Contact a healthcare professional if:
- You have troublesome side effects
- You miss pills and are unsure what to do
- You think you might be pregnant
- You develop symptoms of serious side effects
💡 The combined pill is a safe and effective option for many people when taken correctly. Take your pill at the same time every day and read the information leaflet provided in your pill pack. If you have any questions or concerns, speak to your doctor. Understanding how to use the pill, what to expect, and when to seek advice will help you get the most benefit while staying safe.
Sources & References
This leaflet is based on guidance from the National Institute for Health and Care Excellence (NICE), the Royal College of Obstetricians and Gynaecologists (RCOG), and the NHS.
It is intended as general information and does not replace personalised medical advice.
Last reviewed April 2026 · Always speak to a qualified healthcare professional before starting, changing, or stopping contraception · NHS.uk · NICE.org.uk · RCOG.org.uk