Family doctor


Sexual Health

ORAL CONTRACEPTIVE PILL - a patient's guide


The Pill has been used by most sexually active women at some time. This article provides a broad overview of how it works, and the risks and benefits of its use.


  • The pill is officially known as the combined oral contraceptive pill
  • It combines two synthetic female hormones to prevent conception
  • The pill works by stopping the ovaries from producing eggs
  • There is a failure rate of up to three percent on the pill
  • The most important pills not to miss are those just before and after the 7-day break
  • Some medications reduce the pill's effectiveness
  • Common side effects include breakthrough bleeding, weight change, and nausea
  • Serious side effects include an increased risk of blood clots, and a small risk of breast cancer and heart disease

Key Points:

The term "the pill" used here refers to the combined oral contraceptive pill (COC) where two synthetic hormones, closely resembling the naturally occurring female hormone oestrogen and progesterone, are combined into one pill. Another type of oral contraception pill contains just one synthetic female hormone and is referred to here as "the mini-pill".

The pill works mainly by putting your ovaries to sleep. It fools the ovaries into thinking you are pregnant so that egg-production stops. You cannot get pregnant without eggs being produced by the ovaries. Used properly the pill has a failure rate of between 0.1 to 3%.

On average it takes seven days of taking the pill before the ovaries are asleep. The reverse also seems to be true. Once you stop taking the pill it takes an average of seven days for the ovaries to "wake-up" and start producing eggs again. This allows for the design of pill packages with seven inactive tablets to bring on menstruation.

The pill hormones control the menstrual period that occurs when you are on the pill. The pill takes over control of the special internal lining of your uterus putting it into a resting state. Many oral contraceptive pill packets have seven inactive or dummy pills, which do not contain the hormones. The absence of the pill hormones causes the lining of the uterus to collapse down and bleed. Other pill packaging just misses out seven days of pill taking.

The most important pills in the packet not to miss, are the active hormone pills just before and after the inactive pills.

There are side effects and risks associated with taking the pill. You should try to understand these so that you can make a decision about whether the pill is right for you. Your doctor or contraception nurse can advise you but you are the one who has to make this decision.

What is 'the Pill'?

When we talk about "the pill" here we are meaning the combined oral contraceptive pill (COC). This type of pill has two female hormones combined in each hormone pill. The hormones are made in a laboratory factory to closely resemble your naturally occurring female hormones. Another type of pill "the mini-pill" has just one hormone and is less effective at preventing pregnancy.

The pill was developed back in the 1950s and the first COCs produced contained quite large doses of synthetic hormones. These are called first generation pills and are not used much nowadays. In the 1970s second generation pills were marketed when it was realised that much smaller doses of hormones would still put the ovaries to sleep with less side effects. In the later 1980s new synthetic progesterones were developed and released in third generation pills. These new synthetic progesterones were thought to have less effect on cholesterol and other fats in the bloodstream and therefore reduce the long-term effects of the pill particularly in women who had other risk factors for heart disease.

The pill has played a large role in the sexual revolution that occurred throughout the 1960s and 70s because it allowed women much easier and better control over fertility.

How do I take the Pill?

It is easier to understand the instructions that follow if you have your pill packet in front of you. Different manufacturers package their COCs differently.

Read the instructions in the packet firstly to find out if it is a 28-day packet or a 21 day packet. 21 day pill packets just miss out the inactive pills.

When you first start taking the pill it is easier to wait for your next period to start. However remember to use other contraception or avoid intercourse while you are waiting and for 12 days after first starting the pill. (Although 7 days of active hormone pills can put the ovaries to sleep, it is wise to build in a margin of a few days when you first begin the pill.)

On the first day of bleeding take your first pill from the marked starting area on the packet. Read the instructions to find this. Take the pill marked with the right day of the week. The active pills are the hormone pills. These hormone pills get broken down inside the stomach and the hormones pass into the blood and travel to the ovaries.

28 day packages have 7 dummy pills. These are just there to remind you to take a pill every day and to bring on a period. It is most important to make sure you are off hormone pills for no longer than 7 days. Otherwise the ovaries will 'wake up' and you may get pregnant a week or two later. So it is crucial not to be late starting the active hormone pills after taking the inactive pills.

Take one pill each day following the arrows until your pack is finished.

It is a good idea to try and take your pill at about the same time every day. However you have not officially 'missed' a pill until you are more than 12 hours past the normal time you take your pill.

When you start the inactive dummy pills, the lining of your womb is deprived of the hormones that are keeping it in a resting state and collapses down and bleeds. This occurs 2-4 days into the inactive pills. When you again begin the active hormone pills, the lining of your womb goes back to the resting state and stops bleeding. Menstruation on the pill is normally lighter than a naturally occurring period.

Your next pack

Start your next pack the day after you finish your last pack.

Do not miss a day and do not wait for your next period to begin.

Start every pack in the same section on the right day of the week.

What is the 7-day rule?

The '7 day rule' is based on the following:

When you first start taking the pill it takes about 7 days for the pill hormone to put the ovaries to 'sleep'. So if it seems that the pill may have been missed, or not been absorbed properly, and the ovaries might have 'awakened'. keep taking the pill for 7 days without trusting it. Then the ovaries should be back to sleep.

The times to use the 7 day rule are when you:

Miss an active hormone pill or take it more than 12 hours after the usual time.

Vomit within 4 hours of taking your pill or have continued vomiting (the pill might not be absorbed).

Have diarrhoea (the pill might not be absorbed).

Are taking other medications such as antibiotics, medication for epilepsy, laxatives, rifampicin for Tb or meningitis.(make sure your doctor knows you are on the pill before you are given any other medicines to take).

If any of these things happen, you need to follow the 7-day rule

How to use the 7- day rule:

Take your (last) forgotten pill immediately and then keep taking your pills on the days marked on the packet.

You will not be safe from pregnancy until you have taken 7 active hormone pills in a row.

Use another method of contraception such as condoms or do not have sex until you have taken the 7 active hormone pills.

If you are taking other medications such as those we have mentioned or if you have vomiting or diarrhoea, you need to use another method of contraception during this time and for 7 active hormone pills in a row afterwards.

If you miss more than one hormone pill, say over Tuesday, Wednesday, Thursday and you realise this on Thursday, take Thursday's pill and then apply the 7 day rule.

The next bit is harder to understand and you will need to study your pill packet while reading the following;

If you missed your pill or had vomiting or diarrhoea or took the other medications during the time you were taking the 7 hormone pills which come in the packet just before the inactive dummy pills , then you should miss out the dummy pills from that packet. This is just to make sure that the 7 days on the dummy pills will not be 8 or 9 days off hormones thus resulting in the ovaries 'waking up'.

You should go straight from the last active hormone pill of that packet onto the first active hormone pill in the next packet

If you do this you will not have a period that month but there is no harm to your body from missing a period now and then using this method and it does not mean that you are pregnant. It is not recommended that you miss a period every month.

If you missed your pill or had vomiting or diarrhoea, or took the other medications and have had sex, and you have FORGOTTEN TO USE THE 7 DAY RULE, you can use EMERGENCY CONTRACEPTION (what used to be called the 'morning after pill), as long as you start taking it within 72 hours of having had sex.

What can I expect on the Pill?

Some women notice changes especially when first starting the pill.

You may experience one or two of the following side effects (which imitate some of the feelings women have in early pregnancy). These usually improve or go away within 3 months. If they persist you can try another pill to see if it suits you better, but talk to your doctor or nurse before stopping your pill.

  • Bleeding between periods may occur for a month or two after starting the pill. This is called "breakthrough" bleeding and usually settles after 1-2 months.
  • Breast tenderness
  • Nausea -if you feel sick, taking your pill with food can help.
  • Headaches
  • Weight changes - can be a weight loss or gain.
  • Mood changes
  • Skin changes - sometimes a dark pigment can form on parts of the face for a few people.
  • Reduced libido - (desire for sex.)

What about the side effects and dangers of the Pill?

Serious side effects are rare

The following things may suggest serious disease and you should contact your Doctor if you:

  • Get sudden chest pain
  • Cough up blood
  • Have a pain in the lower leg
  • Have a severe headache
  • Have heavy or prolonged bleeding while taking your hormone pills

The pill has been watched closely over the years to see if it is dangerous for some women. In particular it has been studied to see if it causes increased risks of cancer in hormone-receptive parts of the body such as the breasts, the vagina and cervix and the uterus and ovaries. Another worry has been whether it increases the risk of blood clots forming in the legs and travelling to the lungs. This is called a pulmonary embolus and can be fatal. We know that pulmonary embolus is more likely to happen naturally to women during pregnancy and particularly in the week or so after giving birth. The pill has also been watched to see if it increases the risk of heart attacks in older women.

The studies on cancer suggest:

Women on the pill are less likely to get cancer of the womb and ovaries. The risk of developing either of these cancers are reduced by one-half to one-third by the pill and the protective effect can persist for 10 to 15 years after stopping the pill.

There does appear to be a slightly increased risk of breast cancer for women on the pill. On stopping the pill this slight excess risk gradually disappears over 10 years. If breast cancer appears while on the pill it is likely to be slower to progress than a breast cancer occurring in a woman not on the pill. For 1000 women aged 45 who took the pill up to age 35 there would be 1 extra case of breast cancer expected compared with 1000 45 year-old women who had never taken the pill.

Changes to cervical skin cells suggesting that cancer might later occur, are more common for women on the pill. However, it is uncertain whether this is due to the pill itself or due to some factor picked up from male partners during sex. Women who are on the pill tend to have more sex with more partners than women not on the pill. Condoms can provide protection against this male factor.

The studies on clots in the legs suggest:

Women who are not on the pill and are not pregnant have a risk of a deep leg vein clot of approximately 1 per 30,000 women per year if they are non-smokers. Smoking increases the risk, as does obesity. A deep leg vein clot has a chance of breaking away from the vein wall and travelling to the lung which can be fatal (pulmonary embolism). Only a proportion of deep leg vein clots do break away. The overall mortality from deep vein leg clots is about 1-2%. There is not the same risk for a clot in a superficial leg vein visible just under the skin.

Pregnant women have a risk of a deep leg vein clot of 1 per 1000 women per year.

In the week after childbirth the risk is 1 per 500 women per year.

Women who are taking what are called "second generation pills" containing a synthetic progesterone called levonorgestrel, have a risk of approximately 1 per 10,000 per year.

Women who are taking newer "third generation pills" have a risk of approximately 2 per 10,000 per year. However these newer pills may have less effect on future risks of heart disease.

The studies on heart disease suggest:

There appears to be a small increase in risk of a heart attack in middle age for women who take the pill for several years and smoke, compared with women who are non-smokers on the pill or smokers not on the pill.

Other points:

Doctors tend to avoid prescribing the combined pill in women who are very obese, or smoke heavily, have a family history of abnormal blood clots, have high blood pressure, have had clots in varicose veins or have certain types of migraines.

There is an occasional woman who will get high blood pressure on the pill never having had it previously. This may not cause any symptoms, so your doctor or nurse will want to check your blood pressure again after you have been on the pill for 2-3 months to make sure it remains normal.

The pill does not seem to be a cause of long-term infertility in itself. However many women have a delay in menstruation after stopping the pill.

The pill can theoretically be continued up to age 50 for non-smoking healthy women without any risk-factors. However smokers should have a cut-off age of about 35 years.

See also:

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