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).

At a glance: the combined pill

• 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.

Advantages and disadvantages

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

Risks of taking the combined pill

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.