Mirena Side Effect Profile: Percentages
The most common side effects of the Mirena levonorgestrel intrauterine system are bleeding pattern changes, with approximately 50% of users experiencing amenorrhea or oligomenorrhea by 2 years of use, and initial irregular bleeding/spotting expected in the first 3-6 months that generally decreases over time.
Bleeding Pattern Changes
The dominant side effect category for Mirena (LNG-IUD) involves menstrual bleeding alterations 1:
- Amenorrhea or oligomenorrhea: Approximately 50% of users by 2 years of use
- Initial irregular bleeding/spotting: Expected during the first 3-6 months in most users, though specific percentages are not quantified in guidelines
- Amenorrhea rates: 39% at both years 7 and 8 of extended use 2
These bleeding changes are generally not harmful and represent the expected pharmacologic effect of the device 1.
Hormonal Side Effects
Recent high-quality data from a large phase 3 trial (n=1,714) provides specific percentages for hormone-related side effects 3:
- Acne: Reported in 13.0% of users over the first 180 days (particularly those transitioning from combined hormonal contraception)
- All other hormone-related side effects: Each occurred in less than 3% of users during the first 180 days
- Orgasm/libido problems: 3.1% at 360 days (among prior combined hormonal contraception users)
Importantly, only 5.5% of users discontinued due to these hormone-related side effects 3.
Mechanical Complications
From extended safety data through 8 years of use 2, 4:
- Expulsion: 4.1% overall (cumulative through 8 years)
- Perforation: 0.1% (extremely rare, with none occurring after year 1)
- Pelvic infection: 0.9% during device use
Treatment-Emergent Adverse Events
In the Mirena Extension Trial evaluating years 6-8 of use 4:
- Any treatment-emergent adverse event: 68.8% of participants
- Events considered device-related: 18.0%
- Discontinuation rate: 38.4% (though most commonly due to desire for pregnancy at 12.2%, not side effects)
Discontinuation Due to Bleeding
Bleeding complaints leading to discontinuation are notably low 2:
- Overall discontinuation for bleeding: 2.6% across all years
- Years 3-8: Only 0.1-0.5% per year
- Years 7-8 combined: Only 4 total discontinuations for bleeding
Clinical Context and Counseling Points
Critical counseling elements before insertion 1:
- Unscheduled spotting or light bleeding is expected during the first 3-6 months
- Bleeding generally decreases with continued use
- Many women will experience light menstrual bleeding or amenorrhea over time
- Heavy or prolonged bleeding is uncommon during LNG-IUD use
Common pitfall: Failure to adequately counsel about expected bleeding changes is associated with higher discontinuation rates. Enhanced counseling about bleeding patterns and reassurance that irregularities are generally not harmful has been shown to reduce discontinuation 1.
User satisfaction remains high: At the end of year 8, 98.7% of participants who completed extended use studies remained satisfied with the device 4.
The side effect profile strongly favors continuation, with the benefits of highly effective contraception (Pearl Index 0.13, pregnancy rates <1%) 5 far outweighing the primarily benign and self-limited side effects, particularly bleeding pattern changes that many users find acceptable or even beneficial.