Contraceptive pills - your guide

Contraception, or ‘birth control’, is a way for men and women to prevent unwanted pregnancies and plan their families. There are many different methods of contraception, including hormonal contraception (HC) such as the combined contraceptive pill, known simply as "the Pill".

The Pill is taken by mouth by the woman to prevent pregnancy and, when taken correctly, is over 99% effective. However, the Pill does not protect against sexually transmitted infections (STIs), including HIV (the virus that causes AIDS). The latex male condom provides the best protection from most STIs. Other types of combined oestrogen and progestogen hormonal contraception include the contraceptive patch and the vaginal ring.

How does hormonal contraception work?

Normally, a woman becomes pregnant when an egg is released from her ovary (the organ that holds her eggs) and fertilised by a man's sperm. The fertilised egg attaches to the woman's womb (uterus), where it receives nourishment and develops into a baby. Hormones in the woman's body control the release of the egg from the ovary and prepare the body to accept the fertilised egg.

Hormonal contraceptives (the pill, the patch and the vaginal ring) all contain a small amount of synthetic oestrogen and progestogen hormones. These hormones work to inhibit the body's natural cyclical hormones to prevent pregnancy. Pregnancy is prevented by a combination of factors. The HC usually stops the body from releasing an egg from the ovary. HC also changes the cervical mucous to make it difficult for the sperm to find an egg. HC can also prevent pregnancy by making the lining of the womb inhospitable for implantation.

A new option for the HC is extended-cycle pill use, which contains the same hormones as in other birth control pills, but they are taken in a longer cycle to reduce the number of yearly menstrual periods from 13 periods a year to only four periods a year. Therefore, women menstruate only once each season.

Extended-cycle pills contain the same combination of two hormones commonly used in other hormonal contraceptives, and are taken in low doses continuously for 12 weeks followed by one week of inactive pills, which triggers a menstrual cycle.

What are ‘mini pills’?

These are pills that contain only one hormone (progestogen), and are subsequently sometimes known as ‘progestogen-only pills’ or POP. They do not contain oestrogen and may therefore be prescribed to women who are breastfeeding or who experience nausea with oestrogen.

How do mini pills work?

Mini pills work by thickening the cervical mucous so the sperm cannot reach the egg. The hormone in the pills also changes the lining of the uterus, so that implantation of a fertilised egg is much less likely to occur. In some cases, mini pills stop ovulation (the release of an egg). One pill is taken every day within a specific three-hour time slot.