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How a Mirena IUD works as a Contraceptive and Mirena Side Effects

Updated on April 9, 2013

What is a Mirena?

A Mirena is a small contraceptive device shaped like a ‘T’ that is inserted into a woman’s womb in a similar manner to a contraceptive coil. Once inserted it releases Levonorgestrel which is a synthetic version of Progesterone (the female sex hormone)

Mirena Effects

It is used as a contraceptive device, to ease heavy or prolonged menstrual periods which have no known cause (idiopathic menorrhagia) and for protection of the overgrowth of the womb’s lining in women that take Oestrogen only Hormone Replacement Therapy following the Menopause.

Levonorgestrel prevents pregnancy by increasing the thickness of the womb’s natural mucus layer providing a stronger barrier for sperm cells to cross into the womb. Thus reducing the possibility of the sperm causing fertilisation

Levonorgestrel also prevents the thickening of the womb lining in preparation for a fertilised egg cell and stops the egg cell implanting on the wall of the womb to allow development

Key Facts

· A Mirena must only be inserted by a fully qualified, trained Doctor or Nurse.

· Internal examination is necessary prior to insertion so a doctor can check the womb and confirm no pregnancy, infections or sexually transmitted diseases are present.

· The Mirena should only be inserted in the first seven days of a woman’s menstrual cycle (Day 1= the first day of the period)

· An additional contraceptive method such as Condoms will also be required for the first week after insertion.

· A Mirena works for five years

· If a Mirena is fitted as part of HRT treatment it loses its effectiveness after four years

How it works

Mirena Side Effects

Sadly all medicines have possible side effects. Merina side effects often experienced are detailed below

Common Merina Side Effects (affect around 10%)

  • Change in menstrual bleeding, such as spotting, lighter bleeding or complete stoppage
  • Cysts development in the ovaries.

Side effects of Merina affecting 1-10%

· Symptoms of depression

· Migraines and headaches

· Decreased libido

· Abdominal pains

· Period Pains

· Inflammation or discharge

· Acne development

· Potential weight gain

Less Common Merina Side Effects (less than 1%)

· Increased hair growth or hair loss

· Skin reactions such as rashes

· Inflammation of feminine areas

· Bloating

· Swelling from fluid retention (Oedema)

A very rare side effect Merina causes is perforation of the womb (less than 0.1%)

Please be aware

· Insertion and removal can be painful. A painkiller such as paracetamol may assist

· Severe pain may be as a result of the Mirena perforation the wall of the womb. You must let your doctor know straight away if this occurs

· The Mirena can become dislodged without a user noticing. This may lead to increased menstrual bleeding and decreased effect. Therefore the removal threads should be checked regularly

· A regular Mirena side effect is irregular bleeding for the first few months post insertion. This will settle down as periods become lighter or potentially stop altogether.

· A Mirena will NOT protect against STI’s (Sexually Transmitted Infections)


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