The combined pill is usually just called the pill. It contains two hormones - an oestrogen and a progestogen. These are similar to the natural hormones women produce in their ovaries. There are a variety of types of combined pill.

How effective is the pill?
How effective any contraceptive is depends on how old you are, how often you have sex and whether you follow the instructions.

If 100 sexually active women don't use any contraception, 80 to 90 will become pregnant in a year. If the pill is taken according to instructions it is over 99% effective. This means that less than one woman in 100 will get pregnant in a year. If the pill is not taken according to instructions, more women will become pregnant.

How does the pill work?
The main way the pill works is:

• It stops your ovaries releasing an egg each month (ovulation). It also:
• Thickens the mucus from your cervix. This makes it difficult for sperm to move through it and reach an egg.
• Makes the lining of your womb thinner so it is less likely to accept a fertilised egg.

Can anyone use the pill?
Not everyone can use the combined pill and your doctor or nurse will need to ask you about your own and your family's medical history. Do mention any illness or operations you have had. Some of the conditions that may mean you should not use the combined pill are:

• you think you might already be pregnant
• you smoke and are 35 or older

• thrombosis (blood clots) in any vein or artery
• a heart abnormality or circulatory disease, including raised blood pressure
• very severe migraines or migraines with aura
• breast cancer
• active disease of the liver or gall bladder
• diabetes
• unexplained bleeding from your vagina (for example, between periods or after sex)

• doesn't interfere with sex
• usually makes your periods shorter, lighter and less painful
• can help with pre-menstrual symptoms
• protects against two types of cancer - cancer of the ovary and cancer of the womb
• protects against some pelvic infections
• reduces the risk of fibroids (tumours in the womb that are not cancer), ovarian cysts and breast disease that is not cancer

What are the disadvantages of the pill?
You may get temporary side-effects when you first start the pill. These side-effects include:

• headaches
• weight gain or loss
• nausea
• breast tenderness
• bleeding between periods
• mood changes

• the pill may increase your blood pressure
• the pill does not protect you against sexually transmitted infections so you may need to use condoms as well

A very small number of women may develop a blood clot that can block a vein (venous thrombosis) or an artery (arterial thrombosis or heart attack or stroke). If you have ever had a thrombosis, you should not use the pill. Some types of pill appear to be associated with a slightly higher risk of venous thrombosis.

The risk of venous thrombosis is greatest if any of the following apply to you: you are very overweight; are immobile (use a wheelchair); have severe varicose veins, or a member of your immediate family had a venous thrombosis before they were 45.

The risk of arterial thrombosis is greatest if any of the following apply to you: you smoke; have diabetes; have high blood pressure; are very overweight, or a member of your immediate family had a heart attack or stroke before they were 45.

Research shows that women who take the combined pill have an increased risk of being diagnosed with breast cancer. This risk disappears over a ten-year period after stopping the pill. Studies are being done to see why this occurs, and how it relates to pill use, or if women taking the pill are diagnosed earlier than women who don't take the pill.

There is also some research to suggest a link between using the pill and developing cervical cancer, as not using a barrier method of contraception increases your chance of exposure to high-risk strains of the human papilloma viruses (HPV) that are the underlying cause of cervical cancer.

Some research suggests a link between using the combined pill and developing a very rare liver cancer.

Over the years the pill has often been blamed for side-effects that were due to other causes. For most women the benefits of the pill outweigh the possible risks.

See a doctor straightaway if you have any of the following:

• pain in the chest, including any sharp pain which is worse when you breathe in
• breathlessness, or you cough up blood
• painful swelling in your leg(s)
• weakness, numbness, or bad 'pins and needles' of an arm or leg
• severe stomach pains
• a bad fainting attack, or you collapse
• unusual headaches or migraines that are worse than usual
• sudden problems with your speech or eyesight
• jaundice (yellowing skin or yellowing eyes)