Boots WebMD Partners in Health
Return To Boots

Contraception health centre

IUD and IUS: Intrauterine device and intrauterine system

What are IUDs and IUSs?

IUDs and IUSs are both long-acting reversible contraceptive (LARC) methods.

An IUD, or intrauterine device, is a small, plastic and copper, flexible, T-shaped device that is placed into the uterus (womb) for contraception. There are various sizes and types of IUD available to suit the needs of different women. They can remain in the uterus for five to 10 years, depending on the type.

An IUS, or intrauterine system, is a small, T-shaped plastic device that contains progestogen. In the UK the brand name is Mirena, and the system can remain in the uterus for up to five years.

How do they work?

IUDs contain copper, which is slowly released into the uterine cavity. The copper stops the sperm from making it through the vagina and uterus to reach the egg, thus preventing fertilisation.

IUSs, such as Mirena, release the hormone progestogen, which causes the cervical mucous to become thicker so the sperm is less likely to reach the egg. The hormone also changes the lining of the uterus, so implantation of a fertilised egg is less likely to occur. This type of IUS must be replaced every five years.

How effective are the IUD and IUS?

IUDs and IUSs are over 99% effective.

How is an IUD or IUS used?

Once the IUD or IUS has been inserted by your doctor, you do not need to take any further steps to prevent pregnancy until it is time to replace it. How long it lasts depends on the type of IUD or IUS you receive.

Are there side effects associated with IUDs and IUSs?

IUDs and IUSs rarely cause serious side effects when used in a monogamous relationship (having only one sex partner). Side effects include pelvic inflammatory disease, painful and heavy periods, backaches, and headaches. Discuss these side effects with your doctor, nurse or family planning expert.

Mirena is associated with lighter menstrual periods.

Do IUDs protect against sexually transmitted infections?

No. IUDs do not protect against sexually transmitted infections (STIs), including HIV (the virus that causes AIDS). The male condom provides the best protection against STIs.

WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on October 10, 2014

Stay informed

Sign up for BootsWebMD's free newsletters.
Sign Up Now!

Popular slideshows & tools on BootsWebMD

agave syrup
These may not be so healthy
exercise illustration
The 7-minute workout
female patient consulting with female GP
How to boost your chances
bowl of soup
Small changes that lead to weight loss
heart rate graphic
What is it, and how is it treated?
smiling woman
Much more than weight loss
crossword puzzle
Tips for the first hard days
sperm and egg
Facts to help you get pregnant
Put your best face forward
sick child
Treating your child's cold & fever
couple makigh salad
How it can help with weight loss
couple watching sunset
How much do you know?