Can I get pregnant on the pill?

Getting pregnant whilst on the pill?

The birth control pill is a popular and effective method of contraception. However, some factors such as missing a pill, vomiting and being on certain medications can reduce the effectiveness of the pill and may result in an unwanted pregnancy.

How effective is the pill?

The combined pill contains hormones that prevent ovulation which is when the ovaries release an egg ready for fertilisation. The minipill, often used while a woman is breastfeeding, causes the cervical mucous to thicken and the uterine lining to thin which limits the sperm from reaching an egg.

The birth control pill is very effective if taken correctly. With perfect use the pill is 99.7% effective.

Reasons for pill failure

  • Missing a day: If a woman misses taking her pill for a day, her hormone levels are affected and may not remain at a consistent enough level to prevent a pregnancy.
  • Not taking the pill at the same time each day.: A woman should take her pill at around the same time each day in order to keep her hormone levels at a consistent level. The minipill only allows a three-hour time window. If a woman misses that window she should use a backup birth control method for the next two weeks such as condoms.
  • Vomiting:  If you become unwell and vomit not long after taking the pill, it may come back up or not be fully absorbed into your system. If you experience vomiting, wait a short while then take another pill.
  • Not starting a new pack when the previous one is completed: It is essential to start you new packet of pills as soon as your finish the previous pack. Missing a few days between packs can make the pill less effective at preventing pregnancy. If a woman misses two or more pills in a row she should use backup contraception or avoid intercourse until she has taken the pill for 14 consecutive days.
  • Medications:  Some medications can make the pill less effective. It is always wise to check with your doctor before commencing any new medication whilst on the pill. Medications can include certain antibiotics and antifungal drugs. Other more long-term medications and supplements that may affect the effectiveness of the pill include some drugs treating epilepsy, anti-viral medications used to treat HIV and a herbal remedy such as St John’s Wort.

Tips for preventing pill failure

  • Take the pill at the same time each day
  • Use an app that tracks periods and provides pill reminders
  • Read the packaging and follow instructions given to you by your doctor
  • Always ensure you have a new packet ready at least a week before your current pack ends
  • Always take a missed pill as soon as possible
  • Use a backup method of contraception such as condoms if you have missed two or more pills in a row.

Birth control pills are very effective if taken correctly and not missed. If you are concerned about remembering to take the pill as recommended, then you should speak to your doctor about other birth control options. There are other options available that do not require taking a pill very day such as an IUD or Implanon implant.


Dr Len Kliman is one of Melbourne’s most experienced and respected obstetricians and gynaecologists.

With over three decades of experience, Dr Kliman has delivered over 20,000 babies and still counting.

In 2017, Dr Kliman was awarded an Order of Australia for his services to obst