The pill is favoured by an estimated 28 percent of UK women that are of reproductive age and is 99 percent effective when used perfectly.

There are several factors that have the potential to disrupt perfect use of the contraceptive pill.

To give yourself the best possible chance of using the pill as safely as possible, it is vital to make sure you follow the points raised below.


To ensure that the pill is working as it should you need to carefully follow the instructions on how to take it.

When you opt to use the pill for the first time you will be advised to start it on the first day of your period.

This is so that you are protected immediately and also ensures that you are not already pregnant. If you decide to start on a different day then you will need to use alternative contraception for the first seven days.

You should also try to take the pill at the same time of day, perhaps after you’ve brushed your teeth or before you go to bed. This way it will eventually become a habit that is hard to forget.

However, if you do forget to take your pill on an occasion then you need to follow the instructions provided with your specific medication. This might include using extra protection or abstaining from sexual contact for the next seven days.

Sickness and Diarrhoea

Sickness and diarrhoea are illnesses that most people experience during their lifetime.

Whilst you’re on the road to recovery, for those who use the contraceptive pill, it is important to remember that it might not be protecting you from pregnancy.

If you are sick within two hours of taking your pill or have severe diarrhoea, where you pass around six to eight stools within 24 hours, then the integrity of your pill may be compromised.

You should take another pill as soon as possible and then resume taking your next pill as you would do normally.

If you’re sick again, or continue to have severe vomiting or diarrhoea, you should count the day as a missed pill day, and use extra protection for the following week.


When two or more medications are used at the same time there is a chance that the combination of ingredients might interact.

This can cause unwanted side effects or reduce the effectiveness of one or both of the drugs. You should be aware that the contraceptive pill can interact with some treatments leaving you unprotected and at risk of pregnancy.

The medications to be aware of include antibiotics, such as rifabutin and rifampicin; anti-epileptic drugs; antiretrovirals and some herbal remedies such as St John’s wort.

You should also be careful if you are using laxatives including some detox drinks, as loose stools can stop the pill from working properly. As mentioned above, diarrhoea symptoms can render the pill ineffective so it is best to consult your doctor prior to starting a new medicine, whether prescribed or over-the-counter.


The contraceptive pill is fairly hardy when it comes to how you should store it but that does not mean that you should neglect it altogether.

The integrity and efficacy of the pill can be disrupted by extreme temperatures and humidity.

If you think that the bathroom cabinet is the best place to keep your pill, then you might want to think again. The heat and humidity could potentially compromise its effectiveness.

You should look to keep your pill packets in a dry place, away from direct light and under 25°C. If you’re heading on holiday it is best practice to keep the pill in your hand luggage. This is because the temperature inside the aircraft hold might drop too low and stop the hormones in the pill from working.

Remember, you should never use medication that has passed its expiration date.


The pill is a very safe method of contraception when used correctly. The list of factors we have compiled here is not completely comprehensive. You should always read the patient information leaflet included with any medication you take before commencing treatment. If you have further questions about external elements that can impact the pill efficacy then you should speak to your doctor.

Page last reviewed:  10/03/2022