How Do Combined Contraceptives Work?

Combined contraceptive pills deliver synthetic oestrogen and progestogen to your body in order to disrupt your normal hormonal balance to affect your reproductive environment. This causes key changes in how your reproductive system works, altering the environment in such a way that it's almost impossible for you to conceive while you take the pill.

What is conception, and how does it happen?

Conception is a complex process that will only happen if all elements come together at precisely the right time in precisely the right environment.

Every month one of your ovaries will release a mature egg, which travels down the fallopian tubes and into the womb. You are at your most fertile at a very specific time during your cycle - the middle point, when you ovulate - which is usually between the 13th and 16th day of your cycle.

Vagina - Diagram of female reproductive system
The hormones prevent the lining from thickening.
The fluid at the neck of the cervix is made
thicker to impede the movement of sperm.
The release of hormones from the pill prevents
ovulation, which is when an egg is
released from the ovaries.


It takes just one sperm to fertilise an egg, despite there being several million sperm contained in semen. When you have sex, these sperm will travel through the cervix, into the uterus and along the fallopian tubes. When you're at your most fertile, you may notice that your vaginal discharge becomes thin and stretchy. This is your body's natural way of making it as easy as possible for sperm to reach your egg.

When the sperm and egg meet, usually in the fallopian tube, a single sperm will penetrate the lining of the egg. This step is known as fertilisation, and it's the first part in the development of an egg.

Once fertilised, the egg travels into the womb, where it plants itself in the womb lining. This lining will have thickened to prepare for a fertilised egg, which it will help develop by supplying hormones that are vital for growth. This is the second stage of fertilisation. Both stages can be prevented through the supply of synthetic hormones, taken orally in the form of combined oral contraceptives.

How do combined contraceptives stop this?

The oestrogen in combined contraceptive pills stops you ovulating because it overrides your natural hormone levels and tricks your body into thinking that ovulation has already happened. This means there's no egg present, so there's nothing for sperm to fertilise. The progestogen thickens the cervical mucus, preventing it from thinning and making it almost impossible for sperm to reach the womb.

At the same time the progestogen also stops the womb lining from developing. This means that in the extremely rare case that an egg has been released and sperm has managed to reach and fertilise it, the egg cannot embed itself to the uterine wall in order to grow.

Myth vs. reality

Many women are put off from the idea of using combined contraceptives because they believe one or many myths surrounding the safety of the pill. The bottom line is that the combined oral contraceptive pill will only be prescribed to you if it's safe for you to use; your doctor won't intentionally put your health at risk and for the vast majority of women, the benefits of combined contraceptives outweigh any risks.

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