How well does an IUS work?
An IUS is over 99% effective at preventing pregnancy.
This means that less than 1 in 100 women using an IUS as their method of contraception get pregnant each year.
Side effects of an IUS
Side effects of an IUS (intrauterine system), also called a hormonal coil, are most common for a few months after having it fitted. Many IUS users do not get any side effects.
Possible side effects include:
- period-like pain and bleeding (spotting) after having an IUS fitted
- small fluid-filled sacs (cysts) on your ovaries – these are usually harmless and disappear without treatment
- a small chance of getting thrush that keeps coming back – talk to your GP if this happens
Some people report headaches, acne, sore breasts, and mood changes. There is not enough evidence to say if an IUS causes these.
If you get any of these symptoms, they should go away within a few months. If side effects are a problem for you, speak to a doctor or nurse.
Your partner should not be able to feel your IUS threads during sex. If they can, see a doctor or nurse to have the threads checked.
How an IUS affects periods
An IUS can make periods shorter or lighter, or stop them altogether.
For 3 to 6 months after having an IUS fitted, your periods might become longer, irregular or more frequent. You may also have some light bleeding between your periods. This should improve within a few months.
If irregular or heavy bleeding continues for longer than 6 months, see your doctor or nurse for a check-up.
Some types of IUS are effective treatments for heavy periods.
Side effects of an IUS as hormone replacement therapy (HRT)
An IUS is sometimes used as part of hormone replacement therapy (HRT) for symptoms of menopause. It has fewer side effects than other kinds of progestogen used for HRT, and can be a good option if you have heavy bleeding when taking HRT.
Find out about choosing a method of contraception, including side effects and risks of different methods.
Risks of an IUS
An IUS is very safe, but there are some rare risks, including:
- pelvic infections, usually within 3 weeks of having an IUS fitted
- your IUS moving or coming out, usually within 3 months of having it fitted
- damage to the womb
- ectopic pregnancy if your IUS fails
Urgent advice: Ask for an urgent GP appointment or get help from NHS 111 if:
You have an IUS and:
- you have pain in your lower tummy (abdomen) and painkillers do not help
- you get sudden pain in your lower tummy that gets worse or does not go away
- you have a high temperature
- you have unusual or smelly discharge
- you have very heavy vaginal bleeding
- you think you might be pregnant
- you cannot feel the threads of your IUS, or they feel different
You can call 111 or get help from 111 online.
Important: If you cannot feel your IUS threads
If you cannot feel the threads when you check for them you might not be protected against pregnancy, and you may need emergency contraception. The IUS can make some types of emergency contraception less effective, so speak to a pharmacist, sexual health clinic, GP or call 111 for advice.
Use another form of contraception until a doctor or nurse has checked your IUS.