What is a mirena?

A mirena is a plastic device measuring around 2cm. It is placed inside the uterus with small strings extending out through the cervix.

When is a mirena used?

A mirena is commonly used for women with heavy periods. More than 80% of women will have an improvement in their periods with the use of mirena. Some women will not menstruate at all.

In New Zealand women with heavy bleeding may qualify for a funded mirena, such as when a blood iron or haemoglobin is found (iron deficient and/or anaemic). Otherwise a mirena costs around $400.

A mirena lasts 5 years. If you are planning pregnancy, the mirena can be removed with use of a speculum, the strings are grasped and the device carefully pulled out. Fertility will return rapidly.

A mirena is also a highly effective contraceptive. It causes contraception in a number of ways:

  • thickening the cervical mucus so sperm cannot enter the uterus
  • stopping sperm reaching the fallopian tube where fertilisation of an egg occurs
  • thinning the lining of the uterus (endometrium) so an embryo cannot implant

The chances of inadvertently falling pregnant when a mirena is inside is less than 1 in 500.

How is a mirena inserted?

A mirena is placed inside the uterus, generally as a procedure when you are awake. Local anaesthetic may be used in the cervix to numb this area. Women generally describe the procedure as uncomfortable. For those who cannot tolerate it being placed awake, a general anaesthetic can be arranged.

Side effects

Common side effects are irregular bleeding, irregular spotting, strings being retained inside the cervix or uterus. Less common side effects are nausea, pain, breast tenderness and headache.

Side effects of mirena will typically settle over 3 to 6 months. You are encouraged to be patient, and to give the mirena 6 months before having it removed.

Further reading

Further information


Bleeding between periods

This is quite common, and if you experience just a single episode you need not be overly concerned. Common causes are oral contraceptives and other hormonal therapies. Persistent bleeding may be caused by genital tract infections, polyps within the uterus or cervix, or possibly cervical cancer. Find out more

Heavy periods

Typically women may menstruate (bleed) for 2-5 days, and lose around 30-40ml of blood. Abnormally heavy bleeding is when: your periods last longer than 7 days; the volume is more than 80ml; there is flooding or clotting; you are anaemic. Find out more


As many as 1 in 6 couples in New Zealand have difficulty falling pregnant. Some causes of infertility in men are issues with sperm quantity and quality. Causes of infertility in women include problems with ovulation, endometriosis, tubal blockage, and issues with egg numbers or quality. Find out more

Irregular or unscheduled bleeding

There are a number of causes of irregular bleeding, and our investigations will depend a bit on your age and fertility plans. Common causes can include endometriosis, infection, instability of the lining of the womb, ovarian cysts, perimenopause, polycystic ovarian syndrome, polyps, and early pregnancy. Find out more

Painful bowel movements

Painful bowel movements (dyschezia) are extremely common. Causes include constipation, anal fissures and irritable bowel syndrome. If you have severe endometriosis, you may suffer from dyschezia during your period. You may also have extremely painful periods and pain with deep intercourse. Find out more

Painful periods

The medical term for painful periods is dysmenorrhoea. You may describe it as pain, discomfort or cramps around the time of menstruation. There are 2 types of dysmenorrhoea: primary and secondary. Find out more

Persistent pelvic pain

If you have pain on and off for more than 6 months we call it 'persistent pelvic pain'. There are a number of conditions that can be involved, and sometimes more than one will be present. In some cases the cause is obvious, such as an ovarian cyst, or a urinary tract infection, but in other women the cause is elusive. Find out more

Prolonged periods

If your period lasts more than 7 days, you have prolonged bleeding. The term is often used synonymously with menorrhogia (heavy bleeding), but is more descriptive of periods that go on for an annoyingly long time. Find out more



Adenomyosis is similar to endometriosis. It occurs when the inside lining of the uterus (endometrium) is found within the muscular wall of the uterus. This may cause the uterus to become enlarged. Adenomyosis may be patchy, or severe, causing a severely enlarged uterus. Find out more


Endometriosis is a common disorder that affects many women in New Zealand. It occurs when endometrial tissue, which should only be found in the uterus, also grows outside the uterus, such as on ovaries or the bowel. This can be very painful and is why women with endometriosis usually have pain around the same time as their period. Find out more