The contraceptive pill is still one of the most successful methods of preventing pregnancy today. But as with any other prescription medicine, how you take it will determine how effective it will be for you.
When used as prescribed, the contraceptive pill can be greater than 99% effective at preventing pregnancy. In numbers, this means less than 1 out of 100 women will get pregnant on the pill each year.
The pill works to prevent pregnancy in three main ways:
- It prevents ovulation (the release of an egg from your ovary) each month.
- It thickens the mucus lining the cervix of your womb, making it difficult for sperm to swim through and fertilise your egg.
- It thins the lining of your womb, making it harder for a fertilised egg to attach to your womb and start growing.
What increases the risk of getting pregnant on the pill?
Certain factors can increase your risk of accidentally becoming pregnant while on the pill, but there are also ways to mitigate these risks.
When you start the pill
In many instances, you will be protected straight away if you start the pill within the first 5 days of your menstrual period. If you start the pill outside these days, you are more likely to become pregnant unless you use an alternative form of contraception, such as condoms, for at least the first 7 days.
Read more: How long does it take the contraceptive pill to work?
Taking the pill at the wrong time
If you take the mini pill, it is important to take it within the time window prescribed for the type of pill you are using. For example, if you usually take it at 6am daily but take it at 12pm one day, this may increase your chance of becoming pregnant. You can set a recurring alarm for the specific time each day to help you take the pill at the right time.
Missing a pill
If you miss more than 2 pills consecutively, you will be at a greater risk of pregnancy, especially if you engage in unprotected sex within the previous 7 days. In this case, continue taking your pills as prescribed but use an additional form of contraception for at least 7 days. You should also seek further advice from your GP.
Feeling unwell
If you experience vomiting or diarrhoea more than 6 times a day, your pill may not be properly absorbed and you may be at risk of getting pregnant. You should keep taking your pills as prescribed, but also seek advice from your GP right away.
Taking other medicines
Some medications, such as antibiotics (particularly rifampicin), HIV and epilepsy medicines, can interact with the pill and increase your chance of becoming pregnant.
You can find out which particular medicines may interact with your contraceptive pill by reading the patient leaflet, which comes with your pill pack, or by asking your GP. It is also important to tell your doctor about any current or new medicines you take, as you continue taking the pill.
Additional resources
What do I do if my contraception fails?
Which contraceptive pill is right for me?
