The combined pill: how it works
Reviewed by the My London Pharmacy clinical team, Yousef Yaghoubi, Pharmacist
·29 July 2026
·8 min read
Quick answer
The combined pill contains two hormones, oestrogen and progestogen, that work together to prevent pregnancy, mainly by stopping ovulation. Taken correctly it is a highly effective, reversible method of contraception, and for many people it also makes periods lighter, more regular and less painful.
How the combined pill works
The combined oral contraceptive pill contains man-made versions of two hormones the body produces naturally: oestrogen and progestogen. Its main action is to prevent ovulation, so that no egg is released each month and there is nothing for sperm to fertilise. Alongside this, it thickens the mucus at the neck of the womb, making it harder for sperm to get through, and it thins the lining of the womb so it is less receptive. These three effects work together, which is part of why the method is so reliable when used well.
When taken correctly and consistently, the combined pill is more than 99% effective, meaning fewer than one in a hundred users would become pregnant over a year of perfect use. In everyday use, where pills are occasionally missed, taken late or affected by illness, effectiveness is closer to 91%, so around nine in a hundred users might become pregnant in a year. That gap between perfect and typical use is the reason taking it reliably, and knowing what to do when something goes wrong, makes such a real difference to how well it protects you.
Types and brands
There are many combined pill brands available in the UK, and although they all work in the same fundamental way, they differ in the type and dose of progestogen and the amount of oestrogen they contain. These differences are why one brand may suit you better than another, and why occasionally a switch is worthwhile if you experience troublesome side effects. Commonly used options include Microgynon and Logynon, alongside other established brands such as Ovranette (Ethinylestradiol / Levonorgestrel), Lizinna (Ethinylestradiol / Norgestimate) and Cilique, and newer formulations such as Eloine, Zoely and Mercilon (Ethinylestradiol / Desogestrel).
Most combined pills are monophasic, meaning every active pill in the pack contains the same dose of hormones, which makes them simple to take and to manage regimens with. A few are phasic, with the hormone levels varying across the pack to more closely mimic a natural cycle. There is no single best pill for everyone: the right choice depends on your health, how you got on with any previous pill, and your own preferences. A clinician can help match a suitable option to you at the start and review it over time, changing it if your circumstances or side effects warrant.
How to take it
A combined pill is usually taken once a day, ideally at around the same time to build a steady habit. Traditionally, packs are taken for 21 days followed by a seven-day break, during which you have a withdrawal bleed that resembles a period. Many pills can also be taken with a shorter break, or run continuously without a break, approaches sometimes called tailored or extended regimens, which reduce the number of bleeds and are now considered safe and reasonable for most people. Some newer packs include inactive or dummy pills so that you take one every day without having to remember when to restart.
When you first start the combined pill, whether you are protected straight away depends on where you are in your menstrual cycle. If you begin on the first day of your period you are usually protected immediately; if you start at another point, you may need to use additional contraception, such as condoms, for the first seven days. Your clinician or the patient information leaflet will explain exactly when your protection begins, so it is worth checking rather than assuming.
Benefits beyond contraception
Beyond preventing pregnancy, the combined pill offers benefits that many people value in their own right. It often makes periods lighter, more predictable and less painful, and it can ease premenstrual symptoms, which is one reason it is sometimes prescribed primarily to help with difficult periods. Some formulations may improve acne, and the pill can be used, under clinical guidance, to help manage conditions such as endometriosis and polycystic ovary syndrome where hormonal control of the cycle is helpful.
Because regimens can be tailored, the combined pill can also be used to delay a period for a holiday, an event or simply for convenience, by running two packs together without the usual break. Over the longer term, combined hormonal contraception is associated with a reduced risk of certain cancers, including cancer of the ovary and the womb, according to national guidance, and this protective effect appears to continue for some years after stopping. These wider benefits sit alongside the contraceptive effect rather than replacing the need for an individual assessment.
Side effects and who can take it
Most people take the combined pill without any problems, but some notice temporary side effects in the first few months, such as headaches, breast tenderness, mild nausea, mood changes or spotting between periods. These commonly settle as the body adjusts, and if they persist a different brand may suit better. The pill carries a small increased risk of blood clots in the veins, which is why it is not suitable for everyone and why a proper assessment is important before starting.
Following the UK medical eligibility criteria that clinicians use, the combined pill may not be recommended if you smoke and are over 35, have migraine with aura, a history of blood clots, very high blood pressure, certain heart conditions, or some other specific health issues, because in these situations the risks can outweigh the benefits. This is precisely why a check of your medical and family history, your blood pressure and your body mass index forms part of starting or continuing the pill. Where the combined pill is not the best fit, a clinician can advise on alternatives such as the progestogen-only pill, which contains no oestrogen, or another method entirely.
What can reduce how well it works
Several everyday situations can lower the pill's protection, and understanding them helps you stay covered. The most common is simply missing pills or taking them late, especially around the pill-free break. Beyond that, severe vomiting within a couple of hours of taking a pill, or very watery diarrhoea lasting more than a day, can stop the hormones being absorbed properly, in which case that pill may not have worked and should be managed like a missed one.
Some medicines can also interfere with the combined pill. These include certain treatments for epilepsy, some medicines for tuberculosis and HIV, and the herbal remedy St John's Wort, which can speed up how quickly the body breaks the hormones down. It is always worth telling any prescriber or pharmacist that you take the combined pill when you start a new medicine, so they can check for interactions and advise on any extra precautions. If you are ever unsure whether your protection has been reduced, using condoms and seeking advice is the safe approach, and the pill does not protect against sexually transmitted infections in any case.
Missed pills and what to do
Missing a pill happens to almost everyone at some point, and what to do depends on how many you have missed and where you are in the pack. As a general rule, if you miss one pill you can take it as soon as you remember, even if that means taking two in one day, and you remain protected. Missing two or more pills, or starting a new pack late, can reduce your protection and may mean you need to use extra precautions such as condoms, and possibly consider emergency contraception if you have had unprotected sex.
Because the precise advice varies with the brand, the number of pills missed and their position in the pack, it is worth reading your patient information leaflet or checking with a pharmacist rather than guessing. Practical habits reduce the chance of missing doses in the first place: keeping the pack somewhere you will see it each day, linking it to a daily routine, and setting a phone reminder all help. Knowing the missed-pill rules in advance means you can act calmly and correctly if it does happen.
Getting started
Starting the combined pill involves a short assessment to make sure it is a safe choice for you. This typically includes questions about your own and your family's health, whether you smoke, and any medicines you take, along with a blood pressure check and a note of your body mass index. None of this is intended to be a barrier; it is simply the information a clinician needs to weigh the benefits against any risks and to choose a suitable brand.
The combined pill is a fully reversible method, so your natural fertility returns after you stop taking it, although it can take a little time for your periods to settle back into their usual pattern. If you would like to start the combined pill, switch brands because of side effects, or review whether it still suits you, our clinical team can carry out a discreet online consultation and advise on a suitable option. NHS sexual health clinics and GP services also provide contraception free of charge, so there are several routes to the method that works best for you.
Frequently asked questions
How effective is the combined pill?
Taken correctly it is over 99% effective. With typical use, allowing for missed or late pills, it is around 91% effective.
Can I take the combined pill without a break?
Many combined pills can be taken continuously or with a shorter break to reduce bleeds. This is safe for most people; a clinician can advise on your brand.
Who should not take the combined pill?
It may not be suitable if you smoke and are over 35, have migraine with aura, high blood pressure, or a history of blood clots. An assessment helps determine suitability.
Can other medicines stop the pill working?
Some can, including certain epilepsy, tuberculosis and HIV medicines and St John's Wort. Tell any prescriber you take the pill so they can advise on precautions.
Does the combined pill affect future fertility?
No. Your natural fertility returns after stopping the pill, though it can take a little time for periods to settle back into their usual pattern.
What should I do if I miss a pill?
Take it as soon as you remember. Missing two or more may reduce protection and require extra precautions: check your leaflet or ask a pharmacist.