How does the hormonal coil work?

The hormonal coil sits in the womb (uterus) and releases small amounts of progestogen, a synthetic hormone similar to the naturally produced progesterone. 

It can stop pregnancy by: 

  • thickening cervical mucus so sperm can’t pass through the vagina to the womb 

  • thinning the womb lining so a fertilised egg can’t implant

In some cases it can also stop you ovulating. But most people will still ovulate – about 75% will keep releasing an egg each month.

Most people will find their periods lighten or stop.

How the hormones affect your body

The coil only releases progestogen in small amounts in the womb. For most people who use it, this means there’s not enough hormone in their blood for it to affect their pituitary gland – which is the bit of the brain in charge of ovulation.

Most people will still go through the natural hormonal changes of the menstrual cycle, and may still get PMS (pre-menstrual syndrome). 

It’s likely that periods will stop, because the hormones thin the lining of the womb. 

Most people have little or no bleeding after a year

As the progestogen in the coil thins the womb lining, there isn’t much blood or tissue to lose with a period. This makes the hormonal coil an option worth considering for people who normally have heavy periods.

How soon does it prevent pregnancy?

If it’s fitted within 7 days of the start of your period, then the hormonal coil is effective immediately. If it’s fitted at any other time of your cycle then you will need to use additional contraception, like condoms, for 7 days.

What does the coil look like?

It’s a small piece of plastic – shaped like the letter T – around 3cm wide across the arms and 3cm long.

Progestogen is stored in the stem of the T shape, covered by a membrane that makes the hormone release slowly and constantly over years.

Types of hormonal coil, and what’s in them

There are several types of hormonal coil. They last for different lengths of time and release hormones at slightly different rates. Here are some examples:


  • Lasts for: 8 years

  • Ingredients: 52 mg of levonorgestrel

  • Release rate: 20 mcg every 24 hours

  • Size: width = 32mm, height = 32mm


  • Lasts for: 5 years

  • Ingredients: 19.5 mg of levonorgestrel

  • Release rate: 17.5 mcg every 24 hours

  • Size: width = 28mm, height = 30 mm


  • Lasts for: 6 years

  • Ingredients: 52 mg of levonorgestrel

  • Release rate: 20 mcg every 24 hours

  • Size: width = 32mm, height = 32mm


  • Lasts for: 3 years

  • Ingredients: 13.5 mg levonorgestrel

  • Release rate: 14 mcg every 24 hours

  • Size: width = 28mm, height = 30mm

Everything you wanted to know about sexual health and wellbeing - your questions answered by our expert team.