Understanding the Mirena Intrauterine System (Mirena IUS)
The Mirena® IUS (intrauterine system) is a small, T-shaped device placed inside the womb (uterus) that slowly releases a hormone called levonorgestrel. it is a hormone-bearing coil that provides long-term protection against pregnancy and can also be used to treat heavy menstrual bleeding and endometrial protection in women on oestrogen replacement therapy.
How does it work?
The Mirena® works mainly by:
- Thickening cervical mucus, making it harder for sperm to reach the egg
- Thinning the lining of the womb, making it less suitable for implantation
- In some cases, stopping ovulation (release of eggs)
It starts working immediately if inserted during the first 7 days of your menstrual cycle.
What are the benefits?
- Highly effective contraception (over 99% effective)
- Long-lasting – works for up to 5 to 8 years, depending on usage
- Can make periods lighter or stop altogether
- Reversible – fertility returns quickly after removal
- May help relieve heavy periods, painful periods, or endometriosis
- Can be used as part of HRT (hormone replacement therapy)
Who can use it?
The Mirena® is suitable for many women, including:
- Those who want long-term contraception
- Women who have heavy or painful periods
- Women who are breastfeeding
- Women who cannot take oestrogen
- Women needing endometrial protection during HRT
Your healthcare provider will check if it’s suitable for you based on your medical history.
What to expect during insertion?
- Insertion is done by a trained clinician during a clinic visit.
- It usually takes only a few minutes.
- You may feel some discomfort or cramping – a painkiller beforehand may help.
- You can usually go home shortly after the procedure.
After the insertion
- Some cramping or light bleeding is normal for a few days.
- Your periods may become irregular or stop entirely over time.
- You will need a follow-up check (usually after 4–6 weeks).
- Check for the threads regularly – your clinician will show you how.
Are there any risks or side effects?
Most women tolerate the Mirena® well, but possible side effects include:
- Irregular bleeding or spotting (common in the first 3–6 months)
- Cramping or pelvic discomfort after insertion
- Headache, breast tenderness, mood changes (usually mild and temporary)
- Small risk of infection (especially within the first 20 days)
- Very rare risk of expulsion (falling out) or perforation (injury to the womb)
When to seek medical advice?
Contact your doctor if you:
- Can’t feel the threads or think the device may have moved
- Experience persistent pain or heavy bleeding
- Have unusual vaginal discharge or signs of infection
- Miss a period and are concerned about pregnancy
Removal and replacement
- The Mirena® can be removed at any time by a trained professional.
- Fertility returns quickly after removal.
- If you wish to continue using Mirena®, it can be replaced during the same visit.
Important to know
- Mirena® does not protect against sexually transmitted infections (STIs) – use condoms for protection.
- Keep track of your menstrual changes and attend all follow-up appointments.