How does the Contraceptive Pill Work?


Combined Contraceptive Pill »

The contraceptive pill is very effective at preventing pregnancy as it has not only one but three mechanisms which all help prevent pregnancy. When used correctly, the pill is over 99% effective but it will not protect you from sexually transmitted infections so extra protection such as condom should be used.

The pill contains two synthetic hormones called oestrogen and progestogen. These are hormones that are very similar to the natural hormones in your body. In your normal menstrual cycle, oestrogen and progestogen levels rise and fall depending on the time of the month, making ovulation occur and preparing the uterus for the chance of pregnancy. If you input a continuous amount of these two hormones into your body, you can trick your uterus into thinking that you have already ovulated. As you only release one egg per month, another egg will not mature and be released so there won’t be an egg present for the sperm to fertilise. This provides a very high form of protection from pregnancy as it stops the egg and sperm meeting in the first place.

The oestrogen and progestogen also have an effect on the mucous lining that is at the opening of your vagina.  This lining protects your vagina from unwanted bacteria and the increased levels of the hormones will cause this to thicken. Creating a thickened mucous lining will essentially create a mucous plug that the sperm will have difficulty penetrating and swimming through. Therefore, the sperms journey is made very difficult so the chances of them reaching the fallopian tubes are slim.  This mechanism also helps reduce the chance of pelvic inflammatory disease as it provides extra protection to the vagina from infection.

The final way the contraceptive pill protects you from pregnancy is by thinning your uterus lining. This lining usually thickens just before ovulation so that if there is fertilization, it is thick enough for the fertilized egg to embed in the uterus wall and grow. Without this joining to the lining, pregnancy would not occur. The levels of hormones stop the uterus lining from becoming thick and keep it relatively thin so in the off chance that the sperm get through the mucous lining and an egg has been released, the fertilized egg would have difficulty securing itself to the uterus wall.

Therefore, the pill is a very effective way of preventing pregnancy. The only way that pregnancy can really occur whilst on the pill is if it has not been taken correctly such as you have forgotten to take some of the pills, medications have interfered with it or you have vomited around the time of taking the pill so it was not fully absorbed into the blood stream.


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