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Medically reviewed by
Dr Daniel Atkinson
GP Clinical Lead
on August 02, 2022.
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What is the pill?

The pill, or combined oral contraceptive pill, works by setting up certain conditions in your body which keep the egg and sperm away from each other. If the two don’t meet, the egg doesn’t get fertilised, and you don’t get pregnant. 

There are a few different types of combined pill, they’re all over 99% effective at providing birth control if you remember to take them at the same time of day, every day. Your contraceptive cover can be compromised if you don’t take the pill at the same time each day.  If you don’t, there’s that odd occasion you’ve forgotten, the pill’s effectiveness drops to 91%. 

So, what is a combination pill? A combined oral contraceptive pill (COCP), has two female hormones in it: oestrogen and progesterone. Oestrogen and progesterone are naturally made in the ovaries. The pill contains synthetic (lab-made) versions. It’s called a ‘combined’ or ‘combination’ pill because it combines these two hormones. 

Oestrogen and progesterone control how and when your body prepares for pregnancy, but more on how the pill stops you from getting pregnant in a moment. As mentioned there are several different types of combined pill. They’re all effective at preventing pregnancy. 

There are three main types of COCP:

Monophasic 21-day pills: all have the same amount of hormone in each pill. One pill is taken each day for 21 days and then no pills for 7 days.

Phasic 21-day pills: are organised into strips with 2 or 3 different coloured sections. The pills in one coloured section contain different amounts of hormones to the pills in a different coloured section. Again, one pill is taken each day for 21 days and then no pills for 7 days.

Every day pills: have 28 pills in one pack. There are 21 active pills and seven dummy pills (although some can contain four dummy pills). One pill is taken each day for 28 days with no break.

When was the contraceptive pill invented?

The first commercially available contraceptive pill was made available in the US in the 1950s. By the 60s it was in full swing and being used by 1.2 million women in America.

The pill was first introduced in the UK in 1961 for married women only. In 1967 the NHS Family Planning Act 1967 was passed and it was available to all women, married and unmarried. A 2019 United Nations report estimated that over 20 percent of women of reproductive age from 27 countries use the contraceptive pill.

How does the combined pill work?

So, what does the pill do and how does the pill work? There are three ways progesterone and oestrogen in the pill work in combination to prevent pregnancy.

Number one: The pill stops ovulation. Once a month you ovulate, your ovaries release an egg that meets a sperm and the egg becomes fertilised. The pill stops ovulation, no egg is released, sperm and egg never meet, and fertilisation doesn’t happen.

Number two: The combined pill makes the mucus in your cervix thicker, so sperm have a much harder time penetrating the womb and reaching the egg.

Number three: The pill thins your uterine lining. The uterine lining builds throughout the month and is what’s dispelled during your period. Normally, the egg is implanted into this lining where it can grow once fertilised. A thin uterine lining means less chance of an egg being implanted into the womb. The benefit of this is that the pill can make periods lighter and more manageable.

How long does it take for the pill to work?

If you’re wondering how long does the pill take to work: you can take it at any time but how long it takes to work will depend on where you are in your cycle.

So, if you take the pill within 5 days after the start of your period, you’re protected from pregnancy right away.

If you start at any other time during your cycle, you’ll be protected from pregnancy after 7 days of using the pill. If you have sex you’ll need to use a condom to protect against pregnancy.

The pill does not protect against sexually transmitted infections, so if you’re starting out with a new sexual partner, it may be a good idea to use a condom whether you’re taking the pill or not.

How effective is the combined pill?

There are two ways of measuring whether a pill is effective at preventing pregnancy. The first is done by ‘Perfect Use’ which is when you take the pill exactly as instructed, every day, without missing a dose. Taken perfectly, the combined contraceptive pill’s effectiveness is 99%.

‘Typical use’ is when someone takes the pill but may occasionally forget to take a dose or take it late. With typical use, the pill is 91% effective at preventing pregnancy. This means that around 9 in 100 women taking it over a year will become pregnant. One clinical study concluded that the pill is “effective, safe and well-tolerated”.

Again, in another study following 900 women in three different countries, Brazil, Egypt and China, there were only four unwanted pregnancies reported, all four because the pill wasn’t taken ‘perfectly’ (every day at around the same time). Similarly, in a study of over 2000 women taking the pill over a year, 19 became pregnant. Fifteen pregnancies of which were due to regularly missing doses or taking doses late.

So, answering, how reliable is the pill? With perfect use, very. However, missing the occasional dose or taking a dose late will affect this, increasing your odds of becoming pregnant by around 9%. The best way to ensure that the pill is as effective as possible at protecting against pregnancy is to take it at the same time every day.

Other things which can impact how effective the pill is include vomiting or diarrhoea, the antibiotic Rifampin, the antifungal Griseofulvin, HIV medicines, anti-seizure medicines, and the supplement St. John’s Wort. Speak with your clinician if you take these before or once prescribed the pill and use a condom as backup protection.

What are the advantages of the pill?

Some combined pills can help make periods more regular, lighter and less painful, ease symptoms of PMS (premenstrual syndrome), and are 99% effective at preventing pregnancy when taken correctly.

Some more advantages of the contraceptive pill include uninterrupted sex without the need to put on a condom, reduced risk of ovarian, endometrial and colon cancer, protection against pelvic inflammatory disease, and a reduced risk of fibroids, ovarian cysts and non-cancerous breast disease.

Some combined pills are also used to treat moderate to severe acne. Talk to your prescriber if you struggle with acne, are taking birth control pills, and have already tried topical treatments and antibiotics. They may be able to recommend a combined pill that can help your acne. It is important to note that the mini pill (progesterone only pill) may make acne worse.

Remember to only take the pill as your clinician advises. If you have any questions while you're taking it, just log into your account and send us a message.

Going on the pill: what’s the right way to start?

There are three possible ways to get started on the pill:

On the first day of your period or the ‘First Day Start’. Here you take your first pill the day you get your period. You’re protected from getting pregnant right away, so you won’t need to use a condom to protect against pregnancy

The ‘Quick start’. Here you take the first pill in your pack when you’re over the five day mark from the day your period started. The hormones in the pill need time to build up in your body, so it will take seven days from starting the pill for it to work. During these 7 days, you’ll need backup contraception, like a condom.

The ‘Sunday start’, for many oral contraceptive pills they’re arranged in the pack by day, starting with Sunday. Here, you take your first pill on the first Sunday after your menstruation starts. You will need to use backup contraception for the first 7 days, like a condom.

When can I start taking the pill after giving birth?

If you’re not breastfeeding: 21 days after giving birth, but check with your doctor or prescriber. If they give you the okay, you will be protected straight away.

If you are breastfeeding, you won’t be prescribed a combination pill. Instead the mini pill is a more suitable alternative.

Using the pill after miscarriage or abortion

If you’ve had a miscarriage or abortion, you can start the pill up to 5 days after this and you will be protected straight away. If you start the pill more than 5 days after, you’ll need to use additional contraception, like a condom, for the first 7 days.

Is the pill safe?

Yes, the pill is safe. This said, it’s common to notice side effects when you start a new pill. These are usually mild and go away after the first two to three months.

A few side effects include nausea, headaches, tender breasts, changes to your mood, bloating and breakthrough bleeding. Breast tenderness and nausea can be reduced by taking your pill before bedtime.

Serious side effects like allergic reactions or blood clots are rare, but you should go to hospital if you have any signs of these. Signs of an allergic reaction include hives, swelling of the face or difficulty breathing. Signs of blood clots include leg pain or swelling, sudden breathlessness, chest pain or irregular heartbeat. Further information on the pill’s side effects can be found in the associated patient leaflet. If you get side effects that are intolerable or don’t go away after a couple of months, speak to your prescriber who may suggest a different pill.

Older research sparked scares over a link between birth control pills and an increased risk of cancer. In fact, the combined pill decreases your risk for ovarian, uterine and colorectal cancers with a protective effect that can last up to 15 years after you stop using birth control. It’s important to familiarise yourself with the pill’s potential side effects before you start taking it.

The pill and the 7-day break: am I still covered?

Yes. You are protected from pregnancy during your combined pill break as long as you start taking your pill again on the 8th day. You must take your pill as you were before (preferably at the same time of day) on the 8th day.

This is because we know that not taking tablets for 7 days weakens the pill’s main effect of preventing your ovaries from releasing an egg; this means that there’s an increased risk that your body will release an egg if you miss your pill on the 8th day.

During your 7 day break on the pill, a lot of women will get ‘withdrawal bleeding’ a lot like getting a period. It’s caused by a break in hormones and isn’t a ‘real’ period. Answering, can I take my pill break early? No. This will increase your likelihood of getting pregnant.

Can I take the combined pill continuously?

Can you take the pill without a break? Yes, it’s safe and can stop monthly bleeding in some women.

Regular monthly bleeds have been found to have no known medical benefits, and by taking the pill continuously you can stop them. Continuous pill taking can also reduce period pain, migraines, other headaches, and is very convenient if there’s a week of the month where you just don’t want to be on your period.

If you do take a break you will likely bleed, like a period, only it’s artificial (caused by a sudden drop in hormones – as you’re not taking them in from the pill) and does not mean that you are not pregnant.

We call this an ‘off-label’ use, which means that whilst the pill isn’t being used exactly as per the manufacturer instructions, it’s safe to use it in this way. Any side effects will be the same as if you were taking the pill with a 7-day break.

Speak with your prescriber before taking the combined pill continuously because it can depend on the type of combined pill you’re taking and they will be able to answer any other questions you may have.

How long can you be on the pill for?

The combined pill can be used as birth control up until you reach the menopause or until you turn 50 years old. This is the same on the regular method or the continuous method.

However, there are a few circumstances where it will be a good idea to discuss being on the pill with your doctor or prescriber. For example, if you develop certain health conditions, there may be a risk that these will interact with the combined pill.

A few examples include a blood-clotting disorder, high blood pressure, heart problems, breast cancer, liver problems, gallbladder disease, migraines with aura (you see bright lines right before your migraine starts), and diabetes.

If you are a smoker over 35 or have just given birth let your prescriber know as they may recommend another form of contraception for you long or short term.

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This page was medically reviewed by Dr Daniel Atkinson, GP Clinical Lead on August 02, 2022. Next review due on August 01, 2024.

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When we present you with stats, data, opinion or a consensus, we’ll tell you where this came from. And we’ll only present data as clinically reliable if it’s come from a reputable source, such as a state or government-funded health body, a peer-reviewed medical journal, or a recognised analytics or data body. Read more in our editorial policy.

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