The combined oral contraceptive pill is usually just called "the pill". It contains artificial versions of female hormones oestrogen and progesterone, which women produce naturally in their ovaries.
When taken correctly, the pill is over 99% effective at preventing pregnancy. This means that fewer than one woman in 100 who use the combined pill as contraception will get pregnant in one year. Other methods, such as the IUD, implant and injection, are more effective.
The usual way to take the pill is to take one every day for 21 days, then stop for seven days, and during this week you have a period-type bleed. You start taking the pill again after seven days.
You need to take the pill at around the same time every day. You could get pregnant if you don't 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.
There is no evidence that the pill makes women 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 for women over 35 who smoke, or women with certain medical conditions.
The pill does not protect against sexually transmitted infections (STIs), so using a condom as well will help to protect you against STIs.