The mini pill contains small amounts of progesterone hormone and is taken by the woman every day. It makes the mucus in the cervix very thick, so sperm cannot enter the uterus to fertilise an egg. If an egg is fertilised, the mini pill also thins the lining of the uterus and slows the passage of the egg down the fallopian tube so it is less likely to implant and survive. For some women it stops ovulation.

The mini pill is about 96% effective, but more than 99% effective if fully breastfeeding and each pill is taken within three hours of the usual time every day. It may not work if you have diarrhoea and/or vomiting, or if taking certain medications (such as antibiotics). Check with your doctor or family planning service. You need to use alternative contraception (such as condoms) while taking the medications, and for seven days after stopping, while continuing to take the mini pill.

Side effects

Possibly irregular menstrual periods or no periods at all, or light spotting between periods. If the mini pill fails to prevent a pregnancy, it is more likely to be ectopic. Let your caregiver know straight away if you think you might be pregnant. Occasionally, the mini pill can cause an ovarian cyst, with low abdominal pain, similar to an ectopic pregnancy. Again, see your doctor. A few women notice a slight weight gain, nausea, headaches and/or a loss of libido.

Breastfeeding

The mini pill can be taken while breastfeeding, but is not started until three to six weeks after giving birth. A very small amount of progesterone can pass through breast milk, but at this stage it is not thought to affect the baby.

Advantages of the mini pill are:

• It can be used instead of the normal pill while breastfeeding. You may choose to swap to the normal pill once you stop breastfeeding, or continue using the mini pill if you prefer.
• It is safer than the normal pill if you smoke, have high blood pressure or a family history of blood clotting abnormalities, strokes or heart attacks.
• It can be stopped at any time to conceive another baby, with fertility returning within two to four weeks.

Disadvantages of the mini pill are:

• It needs to be prescribed by a doctor.
• It is not recommended if you have had a previous ectopic pregnancy.
• You need to be very strict about taking it on time. If you are more than three hours late, take the mini pill when you remember and then take the next one at the usual time. Use alternative contraception (such as condoms) for 48 hours.