The Mirena Intra-Uterine System is an 'intra-uterine coil', containing progesterone, one of the female hormones. It was originally developed as a contraceptive device, for which it is very effective. It is also very effective in improving heavy periods and can be helpful in dealing with some forms of pelvic pain.
It can be particularly useful to reduce the long term risk of endometrial abnormalities when periods are very irregular, in PCOS for instance.
It can often be inserted in the rooms, requiring no anaesthetic, but very occasionally a general anaesthetic might be required. It lasts 5 years, during that time the expectation is that periods will be significantly lighter, such that up to 40% of women may have no periods. It is perfectly safe for periods to stop under the influence of these forms of hormones.
The Mirena can be removed at any time, with full return of normal fertility.