As its name implies the progestogen-only pill (POP) contains only progestogen. It is an alternative to combined hormonal contraceptives (pill, patch or vaginal ring), which contain both oestrogen and a progestogen. The POP is used for women in whom it is preferable to avoid oestrogen. It is not as effective as combined hormonal contraceptives and so is normally prescribed only when there is a reason why the woman is unable to take one of these. The POP is between 90 and 99 per cent effective as a method of contraception.
How does it work?
In some women, the POP completely suppresses ovulation. In others, ovulation may occur each month or only in some months. The progestogen causes the lining of the womb (the endometrium) to become thinner, which decreases the likelihood of a fertilised egg implanting. In addition, the cervical mucus becomes thicker and therefore more resistant to sperm. The motility within the fallopian tubes is also affected so that eggs will have difficulty in passing down the tubes.
What are the advantages of the progestogen-only pill?
- It can be taken by women who are breastfeeding.
- It can be taken at any age (but is often given to women over 35 who smoke or those who cannot take a combined hormonal contraceptive for other reasons).
- It does not raise blood pressure.
- It can help to relieve premenstrual symptoms and often makes periods less painful.
- It is a totally reversible form of contraception.
What are the disadvantages of the progestogen-only pill?
- Some research suggests that the POP may be less effective in women weighing more than 11 stone (70 kg).
- It must be taken at a regular time each day to maintain optimum effect. If its is taken late or if a pill is missed altogether, the contraceptive effect drops markedly. A pill is said to be "missed" if taken three hours later than usual (12 hours for Cerazette® and Cerelle®).
- Some women may experience irregular bleeding or breakthrough bleeding (bleeding between periods).
- As with combined hormonal contraceptives, the POP offers no protection against sexually transmitted diseases, including HIV.
What are the risks of taking the progestogen-only pill?
If fertilisation does occur, there is a small risk that the resultant pregnancy may be ectopic. An ectopic pregnancy is one that develops outside the womb, usually in a fallopian tube. Ectopic pregnancies are rare but can be dangerous - if a period is late and sudden pain develops, medical advice should be sought immediately. The incidence of ectopic pregnancy in women taking a POP is still much lower than in women who were not taking any contraception when they conceived.
A small number of women may develop cysts on the ovaries while taking a POP. These are harmless and will disappear without treatment. In some women cysts will cause pain while in others cysts will not cause any problems.
It is thought that the risk of developing breast cancer in women taking a POP is similar to that in women taking a combined hormonal contraceptive. However, the evidence of a link between breast cancer and the POP is based on a much smaller user population than that for combined hormonal contraceptives and is, therefore, less conclusive.
What are the different types of progestogen-only pill?
The POP is taken every day without a break. The new pack is started the day after the previous pack is finished. A period may still occur as usual but in some women periods may stop altogether. Different tablets contain different levels of progestogen and the doctor prescribing will make a choice about which tablet is the most suitable. POPs that may be prescribed include Aizea®, Cerazette®, Cerelle®, Desomono®, Desorex®, Feanolla®, Nacrez®, Micronor®, Norgeston®, Noriday® and Zelleta®.
Are any regular checks necessary?
The first time the pill is prescribed the doctor will usually give three months supply. If the pill is suitable the doctor will then usually give a six-month supply at the next visit and at subsequent visits. Blood pressure should always be checked when the prescription is renewed. Other screening tests such as regular cervical smears may also be offered. These additional tests are ordered not because the pill is being taken but because the woman taking it is sexually active and may be at risk of sexually transmitted infections.
Further information available from:
FPA (Sexual Health Charity)
23-28 Penn Street
London N1 5DL
Tel: 020 7608 5240
Fact sheet provided by MIMS
Date last reviewed: September 2014