The combined oral contraceptive pill is often just called "the pill". It contains artificial versions of female hormones oestrogen and progesterone, which are produced naturally in the ovaries.

If sperm reaches an egg (ovum), pregnancy can happen. Contraception tries to stop this happening usually by keeping the egg and sperm apart or by stopping the release of an egg (ovulation).

• When taken correctly, the pill is over 99% effective at preventing pregnancy. This means that fewer than 1 in 100 who use the combined pill as contraception will get pregnant in 1 year.
• The standard way to take the pill is to take 1 every day for 21 days, then have a break for 7 days, and during this week you have a bleed like a period. You start taking the pill again after 7 days.
• You may be able to take some types of pill with no or shorter breaks (a tailored regime), which may reduce some side effects. Speak to a doctor or nurse about your options.
• You need to take the pill at around the same time every day. You could get pregnant if you do not do this, or if you miss a pill, or vomit or have severe diarrhoea.
• Some medicines may make the pill less effective. Check with your doctor if you're taking any other tablets.
• If you have heavy periods or painful periods, PMS (premenstrual syndrome) or endometriosis the combined pill may help.
• Minor side effects include mood swings, nausea, breast tenderness and headaches – these usually settle down in a few months.
• There is no evidence that the pill will make you gain weight.
• There's a very low risk of serious side effects, such as blood clots and cervical cancer.
• The combined pill is not suitable if you are over 35 and smoke, or if you have certain medical conditions.
• The pill does not protect against sexually transmitted infections (STIs), so use a condom as well.
• There may be a link between the pill and depression but evidence is mixed and further research is needed.

How it prevents pregnancy

The pill prevents the ovaries from releasing an egg each month (ovulation). It also:

• thickens the mucus in the neck of the womb, so it is harder for sperm to penetrate the womb and reach an egg
• thins the lining of the womb, so there is less chance of a fertilised egg implanting into the womb and being able to grow

The pill is over 99% effective if used correctly. Other methods of contraception are better at preventing pregnancy, such as the IUD, IUS, implant and injection.

There are many different brands of pill, made up of 3 main types:

Monophasic 21-day pills

This is the most common type. Each pill has the same amount of hormone in it. One pill is taken each day for 21 days and then no pills are taken for the next 7 days. Microgynon, Marvelon and Yasmin are examples of this type of pill.

Phasic 21-day pills

Phasic pills contain 2 or 3 sections of different coloured pills in a pack. Each section contains a different amount of hormones. One pill is taken each day for 21 days and then no pills are taken for the next 7 days. Phasic pills need to be taken in the right order. Logynon is an example of this type of pill.

Every day (ED) pills

There are 21 active pills and 7 inactive (dummy) pills in a pack. The two types of pill look different. One pill is taken each day for 28 days with no break between packets of pills. Every day pills need to be taken in the right order. Microgynon ED is an example of this type of pill.

Follow the instructions that come with your packet. If you have any questions, ask a doctor, nurse or pharmacist.

It's important to take the pills as instructed, because missing pills or taking them at the same time as certain medicines may make them less effective.

How to take 21-day pills - standard regime

• Take your 1st pill from the packet marked with the correct day of the week, or the 1st pill of the 1st colour (phasic pills).
• Continue to take a pill at the same time each day until the pack is finished.
• Stop taking pills for 7 days (during these 7 days you will get a bleed).
• Start your next pack of pills on the 8th day, whether you are still bleeding or not. This should be the same day of the week as when you took your 1st pill.

How to take every day pills

• Take the 1st pill from the section of the packet marked "start". This will be an active pill.
• Continue to take a pill every day, in the correct order and preferably at the same time each day, until the pack is finished (28 days).
• During the 7 days of taking the inactive pills, you will get a bleed.
• Start your next pack of pills after you have finished the 1st pack, whether you are still bleeding or not.

Tailored regimes

You can also take the combined pill as a tailored regime. This may include taking the pill for 21 days and stopping for 4, or taking the pill continuously without a break. For more information speak to a doctor or nurse.

Starting the combined pill

You can normally start taking the pill at any point in your menstrual cycle. There is special guidance if you have just had a baby, abortion or miscarriage. The guidance may also be different if you have a short menstrual cycle. Get advice from a doctor or nurse if you need it. You may need to use additional contraception during your 1st days on the pill – this depends on when in your menstrual cycle you start taking it.

Starting on the 1st day of your period

If you start the combined pill on the 1st day of your period (day 1 of your menstrual cycle) you will be protected from pregnancy straight away. You will not need additional contraception.

Starting on the 5th day of your cycle or before

If you start the pill on the 5th day of your period or before, you will still be protected from pregnancy straight away.

Starting after the 5th day of your cycle

You will not be protected from pregnancy straight away and will need additional contraception until you have taken the pill for 7 days.

If you start the pill after the 5th day of your cycle, make sure you have not put yourself at risk of pregnancy since your last period. If you're worried you're pregnant when you start the pill, take a pregnancy test 3 weeks after the last time you had unprotected sex.

If you miss a pill or pills, or you start a pack late, this can make the pill less effective at preventing pregnancy. The chance of getting pregnant after missing a pill or pills depends on:

• when the pills are missed
• how many pills are missed

Find out what to do if you miss a combined pill.

Vomiting and diarrhoea

If you vomit within 3 hours of taking the combined pill, it may not have been fully absorbed into your bloodstream. Take another pill straight away and the next pill at your usual time.

If you continue to be sick, keep using another form of contraception until you've taken the pill again for 7 days without vomiting.

Very severe diarrhoea (6 to 8 watery poos in 24 hours) may also mean that the pill does not work properly. Keep taking your pill as normal, but use additional contraception, such as condoms, while you have diarrhoea and for 2 days after recovering.

Speak to a GP or nurse or call NHS 111 for more information, if your sickness or diarrhoea continues.

If there are no medical reasons why you cannot take the pill, and you do not smoke, you can take the pill until your menopause. However, the pill is not suitable for everyone. To find out whether the pill is right for you, talk to a GP, nurse or pharmacist.

The pill may not be right for you if you:

• are pregnant
• smoke and are 35 or older
• stopped smoking less than a year ago and are 35 or older
• are very overweight
• take certain medicines

The pill may also not be right for you if you have (or have had):

• blood clots in a vein, for example in your leg or lungs
• stroke or any other disease that narrows the arteries
• anyone in your close family having a blood clot under the age of 45
• a heart abnormality or heart disease, including high blood pressure
• severe migraines, especially with aura (warning symptoms)
• breast cancer
• disease of the gallbladder or liver
• diabetes with complications or diabetes for the past 20 years

After having a baby

If you have just had a baby and are not breastfeeding, you can most likely start the pill on day 21 after the birth but you will need to check with a doctor. You will be protected against pregnancy straight away.

If you start the pill later than 21 days after giving birth, you will need additional contraception (such as condoms) for the next 7 days.

If you are breastfeeding, you're not advised to take the combined pill until 6 weeks after the birth.

After a miscarriage or abortion

If you have had a miscarriage or abortion, you can start the pill up to 5 days after this and you will be protected from pregnancy straight away. If you start the pill more than 5 days after the miscarriage or abortion, you'll need to use additional contraception until you have taken the pill for 7 days.

Some advantages of the pill include:

• it does not interrupt sex
• it usually makes your bleeds regular, lighter and less painful
• it reduces your risk of cancer of the ovaries, womb and colon
• it can reduce symptoms of PMS (premenstrual syndrome)
• it can sometimes reduce acne
• it may protect against pelvic inflammatory disease
• it may reduce the risk of fibroids, ovarian cysts and non-cancerous breast disease

Some disadvantages of the pill include:

• it can cause temporary side effects at first, such as headaches, nausea, breast tenderness and mood swings – if these do not go after a few months, it may help to change to a different pill
• it can increase your blood pressure
• it does not protect you against sexually transmitted infections
• breakthrough bleeding and spotting is common in the first few months of using the pill
• it has been linked to an increased risk of some serious health conditions, such as blood clots and breast cancer

The combined pill with other medicines

Some medicines interact with the combined pill and it does not work properly. Some interactions are listed on this page, but it is not a complete list. If you want to check your medicines are safe to take with the combined pill, you can:

• ask a GP, practice nurse or pharmacist
• read the patient information leaflet that comes with your medicine

Antibiotics

The antibiotics rifampicin and rifabutin (which can be used to treat illnesses including tuberculosis and meningitis) can reduce the effectiveness of the combined pill. Other antibiotics do not have this effect.

If you are prescribed rifampicin or rifabutin, you may be advised to change to an alternative contraceptive. If not, you will need to use additional contraception (such as condoms) while taking the antibiotic and for a short time after. Speak to a doctor or nurse for advice.

Epilepsy and HIV medicines, and St John's wort

The combined pill can interact with medicines called enzyme inducers. These speed up the breakdown of hormones by your liver, reducing the effectiveness of the pill.

Examples of enzyme inducers are:

• the epilepsy drugs carbamazepine, oxcarbazepine, phenytoin, phenobarbital, primidone and topiramate
• St John's wort (a herbal remedy)
• antiretroviral medicines used to treat HIV (research suggests that interactions between these medicines and the progestogen-only pill can affect the safety and effectiveness of both)

A GP or nurse may advise you to use an alternative or additional form of contraception while taking any of these medicines.

There are some risks associated with using the combined contraceptive pill. However, these risks are small.

Blood clots

The oestrogen in the pill may cause your blood to clot more readily. If a blood clot develops, it could cause:

• deep vein thrombosis (clot in your leg)
• pulmonary embolus (clot in your lung)
• stroke
• heart attack

The risk of getting a blood clot is very small, but your doctor will check if you have certain risk factors before prescribing the pill.

Cancer

The pill can slightly increase the risk of developing breast cancer and cervical cancer. It can also decrease the risk of developing womb (uterus) cancer, ovarian cancer and bowel cancer.

However, 10 years after you stop taking the pill, your risk of breast cancer and cervical cancer goes back to normal.

Contraception is free to everyone through the NHS. Places where you can get contraception include:

• community contraception clinics
• some genitourinary medicine (GUM) clinics
• sexual health clinics – they also offer contraceptive and STI testing services
• GP surgeries – talk to a GP or nurse
• some young people's services (call the Sexual Health Line on 0300 123 7123 for more information)

Find a sexual health clinic

You can get the combined pill from some pharmacies without seeing a doctor or nurse for a prescription.

Find a pharmacy that offers the contraceptive pill without a prescription

If you want advice about changing your contraceptive pill, you can visit a GP, contraceptive nurse (sometimes called a family planning nurse), or sexual health clinic.

You should not have a break between different packs, so you will usually be advised to start the new pill immediately or wait until the day after you take the last of your old pills.

You may also be advised to use alternative methods of contraception during the changeover, as the new pill may take a short time to take effect.

Contraception services are free and confidential, including for people under the age of 16.

If you're under 16 and want contraception, the doctor, nurse or pharmacist will not tell your parents (or carer) as long as they believe you fully understand the information you're given and your decisions.

Doctors and nurses work under strict guidelines when dealing with people under 16. They'll encourage you to consider telling your parents, but they will not make you.

The only time that a professional might want to tell someone else is if they believe you're at risk of harm, such as abuse. The risk would need to be serious, and they would usually discuss this with you first.

More information

For more information about the pill visit:

• Sexwise's page about the combined pill
• Contraception Choices' page about the combined pill