Can I get pregnant on the contraceptive pill?
Reviewed by our clinical team - 22.9.22
The short answer is yes. No form of contraception is entirely guaranteed (except abstinence) and the pill is no different. However, when taken correctly, it's more than 99% effective.
What are the chances of getting pregnant on the pill?
If used correctly, fewer than 1 woman in 100 who use the contraceptive pill will get pregnant within a year, this is the same for both the combined pill and progestogen-only pill.
How does it work?
The pill alters the menstrual cycle using man-made versions of the female hormones, oestrogen and progesterone.
It works by:
- Stopping ovulation
- Thickening the cervical mucus to make it difficult for sperm to penetrate the womb
- Thinning the lining of the womb to minimise the chances of a fertilised egg being able to grow
There are different types of contraceptive pills available, which work in slightly different ways.
Common pill brands include:
What if I vomit or have diarrhoea?
In some circumstances vomiting and/or diarrhoea can reduce its effectiveness and put you at risk of an unwanted pregnancy. Some drugs and medical conditions have the potential to reduce the effectiveness of contraceptives indirectly by causing diarrhoea or severe vomiting.
If you vomit within three hours of taking your pill (two hours for progestogen-only pills), there’s a chance it hasn’t had time to be absorbed into your body. If this happens you should take another one straight away. Provided you aren’t sick again, you will continue to be protected against pregnancy and should resume your usual routine the following day.
If you're continuously sick or experience severe diarrhoea for more than 24 hours, then its effectiveness may be reduced. In this case, you need to count each day with sickness or diarrhoea as a day you have missed your contraception. Continue taking your pill as normal but use extra protection, like condoms, for seven days after vomiting and/or diarrhoea stops (two days for progestogen-only pills). If you have unprotected sex during this period, you may not be protected against pregnancy.
Can alcohol stop the pill from working?
No. It’s a common myth that alcohol makes the pill less effective, but there’s no evidence that booze directly impacts its performance. However; it might increase the likelihood of you forgetting to take it.
Do antibiotics make the pill less effective?
Most antibiotics are perfectly safe to take with the pill and do not reduce its effectiveness. The exceptions are rifampicin and rifabutin, in addition to the antifungal tablet, griseofulvin.
Am I protected during the break week?
Yes, as long as you have been taking the pills correctly and start the next pack on time.
Signs of pregnancy on the pill
If you’re worried you might be pregnant, symptoms you can check for include:
- Feeling sick, nauseous and/or vomiting (also known as morning sickness)
- Feeling more tired, exhausted or emotional than usual
- Breast soreness or tenderness
- Urinating more often than usual
- Experiencing unusual tastes or being highly sensitive to certain smells
- Having cravings for new or non-typical foods, or losing interest in your usual favourites
If you’re experiencing any of the above and think you may have become pregnant while taking the pill, you should take a pregnancy test and consult your doctor as soon as possible.