How Effective is the Pill?

‘The pill’ is one of the most common forms of contraception used by women today. The pill is taken orally, and comes in two forms: the combined oral contraceptive pill (COCP) and the progesterone-only pill (POP) or ‘mini-pill’.

Combined pills contain synthetic versions of the two hormones produced naturally by the female body: oestrogen and progesterone. The mini-pill contains progesterone only.

Although it’s suitable for many women, there are things that may mean the pill isn’t right for you:

• Certain illnesses
• Health conditions
• Personal/lifestyle factors
• Conditions that run in families
• Some other medications, if you’re also taking these

If you’d like to start taking a contraceptive pill you should discuss with your nurse or doctor which pill would be best for you.

The pill is most effective when taken properly. Different pills will have different instructions for taking them, which you should always follow when possible. If you forget to take the pill or take your usual dose late it can reduce the effectiveness of the pill and put you at risk of getting pregnant.

Both types of pill must be taken regularly in order to protect you against unintended pregnancy. The combined pill is taken once a day, at the same time, for 21 days in a row. This is traditionally followed by a 7-day ‘break’ period when you take no pills before starting the next pack.

However, it’s now recognised that this pill can be taken with shorter, less frequent, or no breaks. It’s best to discuss which regime would suit you best with your prescriber.

The mini-pill should be taken at the same time once every day with no breaks between packs.

If taken correctly, both the combined pill (COCP) and mini pill (POP) are effective in over 99% of cases. This means that fewer than 1 in 100 women taking it in one year will get pregnant.

Traditional mini pills have a shorter window in which they can be taken each day, and theoretically they may be slightly less effective than newer mini pills that contain desogestrel.

Both pills can be started at any point during your menstrual cycle.

Different pills will be effective from different points from when you start taking them:

With the combined pill (COCP), you will be protected against pregnancy immediately if you start taking it anytime from the first to the fifth day of your period. You will not need to use additional types of contraception. If you start your pill on any other day during your menstrual cycle, however, you will need to use condoms or another form of contraception for the first 7 days of taking it before it will be an effective protection against pregnancy.

With the mini-pill or progestogen-only pill (POP), you will also be protected from pregnancy straight away if you start taking it anytime from the first to the fifth day of your menstrual cycle. If you start it any later than the 5th day, you will need to use an additional method of contraception for 48 hours after starting your pill (e.g. until you’re on the third day of taking the mini pill).

The contraceptive pill is a highly effective form of contraception when taken properly. No one contraceptive is 100% effective in preventing pregnancy, and most forms will have some side effects, so it is worth shopping around to work out what will be best for you.

• When used correctly, male condoms are 98% effective and female condoms are 95% effective in preventing pregnancy in every 100 cases per year.
• Latex diaphragms (when used with spermicide) are 94% effective in preventing pregnancy in 100 cases per year.
• One of the benefits of longer-lasting reversible contraceptive (LARC) methods is that they’re more effective than typical, non perfect use of the contraceptive pill. The implant, IUS (intrauterine system) or IUD (intrauterine device) are all more than 99% effective with typical use. The injection is 94% effective with typical use. With perfect use, long-acting reversible contraceptive methods are all more than 99% effective.
• Other forms, such as the contraceptive patch and the vaginal ring, are also more than 99% effective when used correctly, meaning that fewer than 1 in 100 women will get pregnant per year when using them. Female sterilisation and male vasectomy are also more than 99% effective at preventing pregnancy per 100 women per year.

The main advantages of the pill are that it is a fully reversible form of contraception, easy and convenient to take daily.

Certain things can make the contraceptive pill less effective. These include:

• Certain medications: e.g. some antibiotics that belong to a class of medication called enzyme inducers, certain epilepsy and HIV medications and weight loss tablets or laxatives can make your pill less effective. Barrier contraception will be needed to prevent pregnancy. Always check with your doctor whether a medication will interact with your pill and how long barrier protection like condoms will be required.
• Herbal remedies: some herbal supplements and remedies (like St. John’s Wort and high dose Vitamin C tablets) can reduce the effectiveness of the pill. Always check the packet for drug interactions before taking them if you are on the contraceptive pill.
• Illnesses: some infections or fevers can make the pill less effective. If you have severe diarrhoea or vomit soon after taking your usual pill, you may also be at risk of pregnancy.

If you're ever in doubt or unsure whether a pill has worked, it's always better to be extra cautious and use an additional method of contraception alongside the pill for at least 7 days for the combined pill, or 48 hours for the mini pill. If you think you’ve been unprotected against pregnancy and you’ve been sexually active, you may need to take emergency contraception e.g. the morning after pill.