Looking like a letter T, the intrauterine system (IUS) is made from plastic and is fitted into the womb (uterus) by a doctor or nurse. The two types are called Jaydess and Mirena so you may hear it referred to as that.
It releases the hormone progestogen which kills sperm and thickens mucus in the cervix, which makes it hard for sperm to pass through and fertilise an egg. The womb also becomes thinner, which means if an egg were to fertilise, it couldn't attach itself to the womb. It may also prevent ovulation (egg release) in some women.
Extremely convenient as Mirena works for 5 years and Jaydess for 3. It can ease painful and heavy periods and doesn't affect fertility once it's removed. It's also effective, working over 99% of the time.
It can be uncomfortable when first fitted and possible side effects include headaches, skin problems, mood swings and breast pain. There is also a risk of pelvic infections. It doesn't protect against sexually transmitted infections (STIs) so to have safe sex, you will still need to use condoms.
Most women but if you have or have had breast, cervical or womb cancer, have an untreated sexually transmitted infection (STI) or pelvic infection, womb problems, heart, liver disease or stroke seek medical advice as it may not be for you. If you're over 45, it can be left in until the menopause.
Last updated August 1, 2018