The Mirena® coil is generally very well tolerated. It provides reliable protection against pregnancy using a lower dose of hormone than the pill or the three-monthly injection, as it can get to work directly in the womb.
For the first three to six months after having a hormonal coil fitted you may experience side-effects, such as mild abdominal cramps, headaches, breast tenderness, nausea, acne or mood-swings. These symptoms usually improve significantly after this initial period of adaptation. The following table shows the frequency of side effects, during the first few months (the adaptation phase) and afterwards.
￼(Source: Andersson K, Odlind V, Rybo G. Contraception 49: 56-72, 1994)
After the adaptation phase, for every 100 women with the hormonal coil:
- 2 women get abdominal pain; 98 women don’t get abdominal pain
- 1-2 women get headaches; 98-99 women don’t get headaches.
- 1 woman gets mood swings; 99 women don’t get mood swings
- 1-2 women get acne; 98-99 women don’t get acne.
As the hormonal coil primarily works locally in the womb, women continue ovulating and so the moodswings that accompany the menstrual cycle continue too. Women who suffered from mood-swings related to the menstrual cycle before having the Mirena® coil fitted will find that the hormonal coil changes this very little. Mood-swings may be particularly noticeable in women who had previously been taking the pill, as this may have been preventing cyclical mood variations, such as premenstrual syndrome (PMS). However, a woman’s life circumstances often have a greater effect on her psyche than the hormonal contraception does – factors such as stress, double and triple burdens, relationship problems, unresolved conflicts and so on can affect personal wellbeing and it is rare for an emotional imbalance to be caused by the hormonal coil alone.
If you had skin problems before having the hormonal coil fitted, you will probably continue to have them with the Mirena®. If you had been taking the pill, and this was having a positive effect on your skin, you should remember that the hormonal coil contains no oestrogen and so you shouldn’t expect it to have any beneficial effect on your skin.
Figures for the frequency of ovarian cysts vary depending on the method of diagnosis used. In clinical trials, enlarged follicles were found in 12% of Mirena® users. Most follicles are benign and cause no difficulties, and they generally go away by themselves.
Complications from the hormonal coil are very rare. If you have any pain, it may be that the hormonal coil is not positioned correctly. Unexpectedly heavy periods or abdominal pain could, very rarely, be signs of an ectopic pregnancy (which is when a fertilized egg begins to grow outside the womb) or of an injury to the womb. Studies have shown that for every 10 000 women who use the hormonal coil for over a year, there are two ectopic pregnancies – which is as rare as in women who have been sterilized.