In this device levonorgestrel is released directly in to the uterine cavity. The device has mainly a local and hormonal effect including thickening of cervical mucus, prevention of endometrial proliferation and, in some women, suppression of ovulation. The physical presence of the device also may have a minor contraceptive effect.
- in comparison to copper intra-uterine contraceptive devices (IUCD)s, there is a lower risk of ectopic pregnancy and pelvic inflammatory disease. Also pre-existing menorrhagia may be alleviated. The risk of contraceptive failure is superior to that of copper IUCDs and similar to that of sterilisation (about 0.09 per 100 woman-years)
- the Mirena system requires replacing only every five years (1,5)
- the Mirena system can be inserted at any time between day 1 and 7 of the menstrual cycle, from 6 weeks post partum and at any time between day 1 and 5 after first-trimester abortion
- in general, cautions and contra-indications are as for standard IUCDs
- the product is also licensed as a treatment for "idiopathic menorrhagia", with the claim that it "may be particularly useful in women with idiopathic menorrhagia requiring (reversible) contraception" (2)
- expulsion occurs in fewer than 1 in 20 women in five years (5)
- IUS may act predominantly by preventing implantation and sometimes by preventing fertilisation (5)
- no evidence of a delay in the return of fertility following removal or expulsion of the IUS (5)
- the Mirena system is classified as an intra-uterine system (IUS) and not a IUCD
- Mimms, August 1998.
- Mirena. Summary of product characteristics, UK. Schering Health Care Ltd, February 2001
- Drug and Therapeutics Bulletin (2001);39 (11): 85-7.
- BNF 7.3
- NICE (September 2014). Long-acting reversible contraception